At the beginning of each summer, reporters strap themselves into rented Ford Focuses, drive east, stick their pale forefingers in the air and try to decide whether the Hamptons are still hot, or so over.

On Saturday, June 23, at the after-party of the Southampton premiere of the movie Fierce People, legendary adman Jerry Della Femina offered his assessment. “The Hamptons,” Mr. Della Femina declared grandly, “have become a nation unto themselves.

“We have more planes than most countries,” Mr. Della Femina continued. “And you know the chances are we probably are going to attack another country and declare our statehood. Honestly, we have more planes than Costa Rica, so you know we could take them over. We’re gonna have our pledge of allegiance, we’re gonna have our own flag. It’ll be great.”

He was kidding, of course, and yet ….

Hosted by Andrew Saffir, the founder of Cinema Society, an invitation-only screening series, the Fierce People party was a catered, tented and valet-parked affair at a waterfront mansion—whose, no one was quite sure. Despite the ample grounds, revelers were struggling to mingle comfortably among the multiple bars and buffet tables without falling into the nearby pool. There were actor Kelsey Grammer with his wife, Camille; the golden-haired actress Heather Graham; the 1980’s supermodel Rachel Hunter; actress-socialite Dina Merrill with her husband, Ted Hartley; another adman, Donny Deutsch; Warhol muse “Baby” Jane Holzer; as well as the film’s director, Griffin Dunne.

(It was a good turnout, considering publicist Peggy Siegal had organized a premiere of Michael Moore’s new documentary, Sicko, across town at the East Hampton Cinema, followed by a dinner at Prime 103, a swank steakhouse. Her crowd included Mr. Moore, the film’s producer, Harvey Weinstein, designers Donna Karan and Tommy Hilfiger, and comic actor Chevy Chase.)

Meanwhile, Mr. Della Femina, warming to his topic, was anointing a ruler for his prospective principality. “Some day, you know the entire town will be owned by Ralph Lauren,” he said. “King Kullen”—one of the local grocery stores—“will be King Ralph Lauren.”

Typical adman hyperbole! But it’s true that the main streets of both Southampton and East Hampton have abruptly become a platinum-card paradise. At one point, the Hamptons was supposed to be East Coast Malibu; now it’s more like Rodeo Drive in Beverly Hills, or Worth Avenue in Palm Beach. And it’s not just the retail. Rich families have managed to transplant their entire mossy ecosystem from Manhattan: private schools, fancy parties, galleries, museums, theater houses.

“It’s become autonomous,” said the writer and general gadabout Jay McInerney, who was standing at the bar wearing crutches—he broke his foot recently—and a flashy madras blazer. “There are people out here who almost think the city is superfluous.”

Exactly when did the Hamptons become the 51st state?

“It happened very recently,” said Mr. McInerney, before imploring his wife Anne Hearst to fetch him a glass of rosé. “I’m not planning on getting on the L.I.E. for a long time,” he added.

Mr. McInerney is one of that increasing number that no longer makes a distinction between “the season” and the off-season. His children from his marriage with Helen Bransford live in East Hampton and go to the Ross School whose state-of-the-art cafeteria menu features macrobiotic food.

“The schools followed the money—there are like five good private schools out there now,” said Ms. Siegal, whose sister’s family lives in East Hampton full time, over the phone the next day. Her niece also attends the Ross School (which has enrolled 17 new students from the metropolitan area for this coming fall) and her brother-in-law commutes to the city. Ms. Siegal believes that “there is definitely a reverse migration going on” from Manhattan, though she insisted the kind of parties and premieres she hosts have little to do with it. (So humble!)

Regardless, Ms. Siegal has planned six screenings in the Hamptons between now and Labor Day. Mr. Saffir is hosting three, though he could have done “seven or eight,” he said. “The demand is certainly there. Studios are definitely realizing there is a substantive captive audience out here, now more than ever.”

Meanwhile, the Guild Hall theater house in East Hampton is currently undergoing a full 18-month renovation and Southampton’s Parrish Museum of Art is planning an expansion into Water Mill this summer. “Everywhere you look there’s another art gallery opening,” said the writer and longtime Hamptons habitué Steven Gaines over lunch at the American Hotel on June 24. “There’s a lot of new walls to put bad paintings on.”

‘Bad Manners’

Still, arguably no one is more attuned to big money than high-end fashion retailers. Socialite turned fashion designer Tory Burch has a new store, along with John Varvatos, Ralph Lauren’s children’s division and, perhaps most notably, the Elie Tahari outpost on the sunny, suddenly antiseptic corner of Main Street and Newtown Lane. “That building used to house the East Hampton telephone exchange,” Mr. Gaines said ruefully. “And there was a telephone operator, so if you had to make a phone call in the old days, you’d plug in and she’d say yes and she’d do this on the switchboard. And they actually had a cot there, where the telephone operator would sleep, in case somebody had to make a phone call at 2 o’clock in the morning. That building has that kind of history with East Hampton, and now it’s going to be Elie Tahari.”

Not all the new shops are so classy. “The big surprise for all the ladies is T.J. Maxx—that’s the presumptive highlight of the summer,” said Mr. Grammer, this month’s cover subject of Hamptons magazine, at a party honoring the issue at Madame Tong’s earlier Saturday evening. “Everybody goes there! It’s affordable—they’ve always got little treasures in it. My experience with the women is they love to find these treasures.”

Mr. Grammer and his wife Camille, a blond bombshell wearing a precariously short sequined skirt who’s become a champion of irritable-bowel syndrome, have a home in Water Mill. “I know more and more people are living out here full time,” he said. “Our commute is really from California when we come out here. We just skip the city …. We get everything we need here.”

Howard Stern and his fiancée, Beth Ostrosky, may soon be skipping the city, too. “We’re most comfortable here,” said Ms. Ostrosky, in a colorful Missoni blouse and white Hudson jeans, at the Fierce People after-party. “We love everything about the Hamptons, the nature first and foremost. It’s the most magnificent, beautiful spot in the world to us, and we just feel so at home and so at peace here.”

Mr. Stern and his future missus are a year away from completing their enormous dream home in Southampton. “We have our place in the city and we always will,” Ms. Ostrosky said. “But we would be more than happy to be out here and never go back to the city again.”

The king of all media indeed appears at ease in Southampton. That night he drove his black Cadillac Escalade to the front of the mile-long line of cars waiting to be valet-parked, demanded that the check-in table blocking the driveway be moved, and rumbled straight up to the house to drop off Ms. Ostrovsky. He repeated this process when he returned to pick her up. “He said he didn’t want to walk,” said another party guest.

Naturally, not everyone is pleased that the rich folks who used to stop by the Hamptons on the weekend are now leaving deeper footprints.

“This is one of the most beautiful places on earth, and what’s happened to it is slightly sad,” said Susan Forristal, a former model who lives in East Hampton. “Now there are too many young, rich people who have no manners. It’s a very different place now. Too much money. Too many bad manners. It’s not the same place.”

Ms. Forristal, the ex-wife of SNL producer Lorne Michaels, fondly recalled when the towns were populated with “old Jews in Sansabelt pants.”

“My favorite thing was watching Ron and Ellen Delsner fight in line for the movies,” she said. “You could still find a place to buy a needle and thread.” Now there’s an overrun of chic boutiques like Stefani Greenfield’s Scoop. “Which I will boycott until the end of my dying days,” Ms. Forristal said, “because they destroyed our last hardware store.”

But for people like Mr. Grammer and Mr. Stern and, say, Gwyneth Paltrow (who recently annoyed her new neighbors in Amagansett by erecting a giant wall around her manse)—people who aren’t running out to pick up a Philips screwdriver—the Hamptons does have everything. They can trot down to Loaves and Fishes in Bridgehampton and pick up some lobster salad for $100 a pound, or pick up a cappuccino for $6 at Sant Ambroeus. They can peruse the couture produce at the Green Thumb. “Howard and I only eat organic,” Ms. Ostrosky said.

Then again, not everyone is so devoted to clean living.

It was around 2 a.m. on the morning of June 24 at the Pink Elephant nightclub along the Montauk highway. The joint was jumping with pink-cheeked, thirtysomething young men in brightly colored button-down shirts and their female counterparts in this summer’s ubiquitous, unflattering baby-doll dresses, along with Jergens tans.

Owner Rocco Ancarola bragged that numbers for the club are up 30 percent from last year. “I think people are moving out here and they’re finding that they can work out here because everyone has the Internet nowadays, and an apartment on the Bowery—like a one-bedroom apartment—can go for a million or two million!” he said. “Whereas they can come out here and get a really decent house with quality of living. Which is really what life is all about.”