They alight on New York Fashion Week like exotic birds, sending bystanders diving for their cameras. They chirp with one another in the front rows and touch down at the after-parties. Sometimes a few even get loose and jump on the runways: celebrities who love fashion.

This season's shows were no exception. One of the big surprises was the unannounced appearance of Gisele Bündchen, who closed the show at Alexander Wang Saturday wearing an all-black military look: a black leather jacket and a skirt slit nearly thigh high. Unlike some of the other models, she did not wear one of Wang’s fishnet turtlenecks flipped up over her mouth (muzzle-like) although some might have liked to have witnessed that after her post-Super Bowl comments defending husband Tom Brady—and not so much his teammates.

On Monday, just when you thought the Concept Korea show couldn’t feel any more like the dance floor of a crowded club at midnight, in walks actress and musician Taylor Momsen with a ring of photographers. She would be at the brand's after-party later that night too.

At Pamella Roland’s show Tuesday, Extra hostess Maria Menounos—who had an unfortunate Super Bowl incident of her own involving a lost bet and a Giants-colors bikini in Times Square—proved that she was a good sport who could rock evening wear too. She walked the runway in a silver sequined gown with a fishtail bottom that played up her curves.

“Right now the fashion business is more intertwined than ever with the entertainment business,” said Roland, who based her theme for the fall/winter 2012 collection on her family’s favorite ski-vacation spot. In addition to Menounos, she was thoroughly thrilled to have the show open with Carmen Kass, a model from Estonia who has also done Marc Jacobs and Donna Karan runways.

“Carmen opening the show is so strong. She has the most amazing walk,” Roland said.

Good thing, because Kass was to strut past actress Kristin Chenoweth, sportscaster Erin Andrews, and socialite/reality TV personality Tinsley Mortimer, who were among those watching Roland’s models zip by in ski-town numbers like a plaid cape with wool skinny pants and a coyote-fur hood, and sleek gowns such as a strapless emerald-green pleated chiffon beaded gown.

Of course, the celebs were all over town Tuesday. Natalie Portman and Dakota Fanning had prime seats at the Rodarte show at the Metropolitan Pavilion. Over at Bebe Black, Nicole "Snooki" Polizzi of Jersey Shore was in the front row with Angela Simmons and Jill Zarin (who were both at Roland’s show too).

But if you don't subscribe to Women’s Wear Daily or read the fashion and celebrity blogs, do you care?

“I don’t think the average consumer pays much attention to it, but with a fashion brand, it’s about building a relationship with the celebrity for the future,” Susan Ashbrook, author of Will Work for Shoes said. “And that’s the big picture. It’s becoming so competitive now dressing celebrities. It takes time to build a relationship with them, they’re no different than customers.”

But they are different from customers in one important way: Down the road, a celebrity who appears at a particular show or one that goes so far as to walk the runway wearing a particular label’s brand may also appear on the red carpet wearing the brand—a move that gets plenty of press in publications from InStyle to Glamour to Us Weekly.

No one has proved it, says Ashbrook, but years ago, Armani was said to have taken off by bartering with celebrities such as Jodie Foster and Michelle Pfeiffer, who started wearing the brand back in the mid 1980s.

By bartering, Ashbrook means that the stars get the clothing for free and the designer gets the gratis publicity. For young designers just starting out, Ashbrook recommends saying something like, “We can’t afford to pay you for the time, but we’re more than happy to barter for our products.”

After all, just as someone has to be the next Bündchen or Menounos, someone has to be the next Armani.