I EAT, THEREFORE I TWEET, and for no other reason. Without a healthy appetite, I wouldn’t have the stomach for bland and bite-size updates dispatched into the ether by people I’ve never met. But the pig parts man hearts Twitter, and I heart pig parts. So, a grumpy Luddite in the Internet era, I click on his link and follow him online.

If you own a computer and battle sudden cravings for prosciutto cotto, you, too, may be stalking the pig parts man, a former competitive cyclist who now rides for artisan meat producer Boccalone. Every Friday, without any forewarning other than a tweet, he lights out on a bicycle from the company’s Ferry Building salumeria, hauling sandwiches to Twitter-disclosed drop spots around the city. Wherever he turns up, edgy crowds gather in anticipation, like addicts awaiting a fix.

“Have you tried their nduja?” a young man asked me in a whisper that suggested the sidewalk might be bugged.

Until that moment, on a sunny afternoon at 50 Fremont Street, I’d never questioned the depth of my commitment to cured meat. But here I was, confronted by a fervent cultist, a Craig Claiborne wannabe who’d arrived nearly an hour early to claim his place at the front of the line. I was mumbling a response when the crowd began to murmur.

“Tasty salted pig parts!” someone called, parroting the Boccalone slogan. Up rode the cyclist, winded and looking wary, a suitable expression for someone sel­ling street food without a permit. The crowd applauded, then mobbed the bike. There was a whiff of comedy to the mass frenzy. Could any sandwich really be this good?

Of course not. But Boccalone deserves props for its savvy salesmanship, and the sandwich met my basic demands of the genre: Generously stuffed and full of fatty flavor, it featured slivers of prosciutto and provolone, a green layer of arugula, and whole-grain mustard.

I ate mine standing up, propped against a signpost, and marveled at the viral midday madness until a security guard emerged from a nearby lobby and put an end to it.

“See you next time!” the pig parts man announced. Then he pedaled off with a thick fistful of cash, having sold out of his stock and left behind a gaggle of unfed customers.

I felt sorry for them—and they must have felt silly squan­dering their lunch break to miss out on a sandwich that they could have purchased a few blocks away.

REMEMBER OPENTABLE? The quaint website still works if you want a reservation at something called a restaurant. But it won’t ensure your serving of cycle-borne salumi, braised skate cheeks from a Frenchman in a mobile kitchen, or a cured-porchetta sandwich prepared in a warehouse and sold over a counter at a loading dock in Dogpatch.

A new era has arrived, and with it a new aesthetic. Faster than you can say “credit default swap,” restaurateurs have rejiggered their operations, creating fresh delivery systems for escargot-puff lollipops, shrimp po’ boys, and pretty much all edibles in between. Seeking fresh creative outlets and shelter from the downturn, established chefs now do their own PR and their own stunts: serving “underground” dinners from someone else’s kitchen, crafting a roving restaurant out of a revamped taco truck.

They’ve been joined on the streets by a growing fleet of food carts run by home cooks without permits but with free time to Twitter and acquire cult followings of their own. Forage in the Mission district, and you might get a fleeting glimpse of the Magic Curry Man or the Sexy Soup Lady (emphasis on might; flighty from the get-go, the street-cart fad is already showing signs of fading).

Fine dining isn’t dead—it still has its defenders. But if you care for the well-being of a brick-and-mortar business with a black-tie maître d’, odds are you’ve been tempted to call in a priest. It speaks to the times that even Daniel Patterson, the chef-owner of Coi (which earned two Michelin stars last year), is opening two casual outposts: Cane Rosso, a southern Italian takeout joint in the Ferry Building, and Bracina, in Oakland’s Jack London Square.

The scale and speed of the transformation have been stunning. How quickly our attention has turned from scallop sextets at Michael Mina to BBQ pork sandwiches from a loading dock. But we shouldn’t be surprised that change has come. The economic crash has accelerated currents that have long been coursing through the restaurant industry. Once swift enough to carry off white tablecloths, they’re now running so strong that even firm foundations can’t withstand them.

Earlier this year, when the Lark Creek Inn, a restaurant with deep roots in Marin County, recast itself as the Tavern at Lark Creek (buh-bye, $27 petrale sole; hello, rainbow trout for less than $15), you couldn’t blame its owners for bending to the trend. The might­iest of restaurants have betrayed their weakness: Just a few weeks back, former four-star winner Fifth Floor announced that culinary director Laurent Manrique was leaving, and that the kitchen would soon switch from high-concept Gascony cuisine to more accessible (and affordable) American fare. And a few months before that, Aqua (where Manrique is still the corporate executive chef), a stubborn refuge for downtown power lunchers, eliminated its midday menu on every day but Friday. Nearby Perbacco has a different answer: Later this year, expect Barbacco, a more easygoing offshoot of the sleek Italian restaurant, with a soft spot for panini and charcuterie.

Earlier this year, Food & Wine magazine published a defense of haute cuisine that doubled as a lamentation for refinements lost. I don’t get it. It may not be a great time to be Laurent Manrique, but that doesn’t mean it’s a bad time to eat. Call me coldhearted, but I’m unsentimental: We should treat the recent changes like evolution, not global warming. There’s no way we can stop them, and given how good so much of the new food is, I’m not sure we should want to.

NOTHING AGAINST CAVIAR and four-star service—like Kim Jong Il, I still enjoy them. But I felt no pangs of longing for silver flatware when I drifted over to Dogpatch and poked a cornstarch fork into a biodegradable container. Run from a warehouse by a cooperative of chefs (who list Chez Panisse, Incanto, and Eccolo among their alma maters), Kitchenette SF is a Slow Food version of a lunch-pail grab-and-go, and a leading indicator of the setting in which San Franciscans now seem inclined to eat (one of its kindred spirits is Pal’s Take Away, which operates out of modest Tony’s Market in the Mission). By the time I arrived, a small crowd was milling around the load­ing dock, waiting for the metal door to go up and the counter service to begin. It looked like a scene from On the Waterfront, without the waterfront—and no longshoremen, only long-cooked broccoli and a gathering of escapees from nearby offices and live-work lofts. The greens were offered with fromage blanc on a warm baguette, but I opted for the Fatted Calf knockwurst—because I like pasture-raised pork, and besides, that’s what Brando would have done.

True to its pedigree, the knockwurst was plump and flavorful, and it pleased me to consider that the box it came in wouldn’t take up space in a garbage dump. Sitting on a bench in the parking lot out front, I raised a limeade toast to a young man who’d claimed a bench beside mine: just two working stiffs enjoying a manly meal of meat, albeit topped with cucumbers and spring-onion relish. We weren’t in the union, but we were part of the club—and that, it seems to me, is part of Kitchenette SF’s appeal.

Little else stokes the fires of Bay Area food nerds like the feeling that we’re in on something underground. This sense of “discovery” is so compelling that we cling to it, even when we’re told that all the seats are taken, and can we please come back at 9 p.m.? Kitchenette SF is partly a response to the economic climate, but it also plays on our insider delusions. “Spontaneous organic covert nourishment,” reads the motto on its website and menus—a secret lunch spot, advertised only to the billion-plus people on the Internet.

Similar forces have helped propel a recent wave of itinerant restaurants, run by resourceful chefs without a place to hang their aprons, who are teaming up with bar and café owners with extra kitchen space. Marriages of convenience, or perhaps necessity (not all chefs can afford their own restaurants, and rare is the bar owner who turns his back on extra dough), these relationships have produced some compelling pairings, assuming you know where to look. Early operators, such as Radio Africa & Kitchen, a nomadic Mediterranean-inspired restaurant, have been joined by the likes of Melissa Claire’s Kitchen, whose owner and namesake (a veteran of Delfina and Fringale) rents out Velo Rouge Cafe on Thursdays and whips up four-course prix fixe dinners, and Mission Street Food, a hit-or-miss affair that showcases the skills of rotating guest chefs.

That’s far from all: On a recent Thursday evening, I dropped by retro-chic Bruno’s nightclub, an unlikely spot for an Alice Waters sighting. But there she was, the heirloom queen herself, seated in the glow of a bulb-lit Pussycat sign, looking as at home as a pack of frozen spinach at Chez Panisse. She had come to enjoy the debut of Good Evening Thursday, a weekly dinner orchestrated by an accomplished cast. Its ranks included Sam White, a longtime Panisser; former Serpentine and Slow Club chef Chris Kronner; and, according to the email invitation, assorted “friends from a broad range of the food world.” Like the Velvet Revolver of the restaurant circuit, they’d banded together, a San Francisco culinary supergroup (and like most supergroups, it seems the gathering will be short-lived; Kronner says Good Evening Thursday will say goodbye before summer’s end).

Downstairs, the lounge at Bruno’s looked much the same as it always does, except that the bar was serving organic corn dogs and banh mi sandwiches with PC pork. Upstairs, though, candles had been lit, tables had been set atop a leopard-print rug, and a menu had been laid out that listed not just cocktails, but also a $400 pinot noir. Apps and entrées: chopped salad, oysters Rockefeller, prime rib for two—a sophisticated steak house with a speakeasy vibe.

As the night wore on, there were stumbles in the service, a persistent problem at impromptu restaurants, but the food lived up to the polished reputations of the chefs behind it. I ate fish stew—sweet cod, prawns, and clams in a briny broth—and savored my smug sense that I was onto something, a member of the in set, on the leading edge of a dining scene that was transforming before my eyes.

I was in fine spirits all evening. But during my drive home, I started feeling guilty while reflecting on a chat I’d had that very morning with a noted San Francisco chef. The city, he informed me, was “no longer sustainable” for restaurants as we know them. The margins were too slim, and the cost of San Francisco healthcare requirements too high. He envisioned a future stripped of white tablecloths, an uninspired dystopia of casual outposts where number crunchers squeezed the life out of restaurant food.

It all sounded so grim. Where would diners go for refined indulgence? Where would young Escoffiers learn their craft? More to the point, shouldn’t I have canceled my Bruno’s reservation and booked a table at Fleur de Lys?

“Oh, please,” Clark Wolf said. “You think this is something new?” Wolf is a coast-to-coast restaurant consultant, and I’d called him in the hopes that he would assuage my conscience. “Look,” he continued, “why do you think people go out to eat?”

Intrepid marketers like Wolf have invested countless hours and nearly as many dollars seeking answers to that question. Their conclusion ain’t Copernican. “People eat out,” Wolf said, “because they want to feel good.”

Whereas feeling good in boom times meant tuna foie gras towers, today it means sharp, informal cooking—food of highbrow breeding but without the highbrow airs. Foie gras still tastes great, but it seems so out of touch, like a CEO panhandling from a private jet. What we want during the bust is a turkey-meatball sandwich adorned with creamy goat cheese and tangy tomato sauce, like the one I had not long ago at the Sentinel, the stellar takeout spot by Canteen’s Dennis Leary; or an anchovy pizza from the new Pizzeria Del­fina, a retread of Craig Stoll’s Mission district nook that is rightly winning hearts in Pacific Heights.

Restaurants don’t drive changes in the culture; they reflect them. They also adapt quickly—unlike, say, um, the publishing world. Case in point: Laurent Katgely, of Chez Spencer, is now serving escargot and braised skate cheeks from a salvaged taco truck he christened Spencer on the Go!—an inapt name, given that San Francisco’s mobile catering regulations require him to serve from a fixed location. At any rate, Katgely says he’s always wanted to do French food this way. (And Bush II always wanted to invade Iraq, but he also had to wait until the time was right.)

Of course, the current climate will decimate some places. It already has, among them Rubicon, Jack Falstaff, and Jeanty at Jack’s. Not even Jack in the Box has been spared—the one at Mission and Fourth Streets has served its last Jumbo Jack. Tough times, indeed. But restaurants have never been a can’t-miss business, and I found myself agreeing with Wolf’s sanguine perspective. Sure, it’s sad to say goodbye, but each farewell marks a new beginning. The last days of the dinosaurs gave way to the rise of mammals (the only creatures, it should be noted, that are known to gripe about what they eat).

Not that we’ve got the right to grouse, what with all the small, endearing species we’ve seen emerge this year. Blocks from the Panhandle, Nopa gave rise to tiny Nopalito, which in turn has produced some of my most memorable recent meals. Nopalito is a Mexican joint whose humble bearing belies its noble efforts. To enjoy a multilayered mole and a lively michelada mixed with house-ground chilies and slow-roasted tomatoes, I spent less than an hour and under $20, and I left more satisfied than I would have at many restaurants that extract twice the price and inflict three times the fuss.

If anything, the past year has proved that smart res­taurants can downsize without dumbing down. Take Farmerbrown, the spiffed-up San Francisco soul-food place. A few months back, it spawned Little Skillet, serving crisp chicken and waffles and shrimp po’ boys from a takeout window along a SoMa alley. Across town, at Incanto, chef Chris Cosentino has launched a likable Cucina Povera menu on Sundays and Mondays, turning rustic poor-man’s food into fine marketing fod­der. Meantime, ’tis the season for hot dogs and pizza: Pi Bar (get it?), headed for the Mission district, and the new Flour + Water join that neighborhood’s growing list of places specializing in thin-crust pies. And the folks at Foreign Cinema are joining the expanding ranks of wiener vendors with Show Dogs. Their newly opened spot, on Market Street, is devoted solely to pedigree franks. As for power lunches, look to Wexler’s, which opened downtown in June: smoked chicken wings, not tuna tartare, for the suit-and-red-tie crowd.

IN ALL THESE CASUAL NOTES, some hear a requiem for fine dining. But I haven’t placed an order for a funeral veil. Just as demand lingers for Mercedes coupes and Hermès handbags, there will always be a market for haute cuisine. How much of a market is another matter. In San Francisco, we’ll have to don good bifocals to find it.

A more likely spot to look may be across the bay in Oakland—which, lacking San Francisco’s stringent healthcare regulations (S.F. businesses with 20 or more employees are required to provide coverage for their staff), has emerged as an increasingly receptive restaurant frontier. James Syhabout, a celebrated alumnus of PlumpJack Cafe and Manresa, just opened Commis on Piedmont Avenue. Then there’s Charlie Hallowell’s Pizzaiolo, soon to spawn a restaurant on Grand Avenue. In Uptown, one of the city’s rapidly burgeoning gourmet ghettos, Flora, Ozumo, Picán (see Critic’s Table), and Franklin Square Wine Bar have already set up shop.

In San Francisco, the climate is less conducive to taking risks. Even Michael and Lindsay Tusk, of Quince, whose fans would follow them to a Baghdad food court, have wisely hedged their bets in their scheduled crosstown move to a larger space, in Jackson Square. In addition to its usual artful handmade pastas, the new Quince will offer a casual café, called Cotogna, next door.

And so it goes. Just as Barack Obama must now and then eat burgers, restaurants must walk in step with the common man. Take downtown newbie RN74. Though it enjoys the corporate backing of the Mina Group, the kitchen expertise of ex–French Laundry sous-chef Jason Berthold, and a prized location in the Millennium Tower, the restaurant takes great pains not to act high-end. Its setting is industrial, its staff wear blue jeans (the better to signify their Joe the Plumber status), and a ballyhooed wine program (“100 bottles for under $100”) is bargain-basement, provided you got in on the Google IPO.

How far-reaching is the trend? This populist approach has been embraced by none other than Thomas Keller, who took a page from American Idol this year by calling for a flood of public input: A competition was held, with Keller as the judge, to come up with his next restaurant concept.

At the time, I considered submitting a proposal: a French Laundry salmon-cone cart. But then I got wind of the feeble first prize: lunch and dinner for two at Keller’s more casual Ad Hoc. Not that I’m opposed to family-style dining—I’m a down-home guy, just like Joe Biden. But gas was too expensive for the drive to Yountville, and given that I work in a dying profession, I require a fat consultant’s fee.