• Kate Bosworth, mixing with a star-studded

crowd (including Mary-Kate Olsen and Clive Owen)

during a Calvin Klein sponsored bash at New York’s Mercer Kitchen following a screening of her

movie, 21. The actress was happy to hang out with Helena

Christensen as revelers feasted on salmon, French fries and lots of cookies and pastries in the underground restaurant. Meanwhile, Olsen stayed deep in conversation with friend Derek Blasberg - tucked away in the back - and 21 star Jim Sturgess stuck close with his girlfriend, Mickey O’Brien. Later, the crowd moved to Submercer, a tiny subterranean bar that guests could enter from inside the restaurant - continuing the celebrations late into the night.

• Kristen Bell, spending an afternoon with

three friends, taking the backlot tram tour at Universal Studios Hollywood.

• Adrien Brody, casually checking out art with a male friend

at the Armory Show preview party in New York. Also there (separately): Matt Dillon, discussing specific pieces with dealers and looking very

intense as he checked out the art.

• Jennifer Aniston, Courteney Cox Arquette, Eva Longoria Parker and

Orlando Bloom, chatting over chips and guacamole in an

upstairs VIP booth at a party in Hollywood to raise awareness for the

Epidermolysis Bullosa Medical Research Foundation.Meanwhile, downstairs at Longoria Parker’s new restaurant Beso: Host Ken Paves caught up with clients Jessica and Ashlee Simpson over pizza in the booth they shared with pals CaCee Cobb and boyfriend Donald Faison. And nearby, Kate Beckinsale and director husband Len Wiseman shared their booth with Rose McGowan and her director fiancé Robert Rodriguez.

• By LISA INGRASSIA, MARISA LAUDADIO, MELISSA LIEBLING-GOLDBERG and

JEFFREY SLONIM

Celebrity Hot Spots.

Thursday’s Caught in the Act >

• Kate Bosworth, cooling off with some Pinkberry frozen

yogurt with friends in Los Angeles. That same day, the actress and three

friends hit up Mauro’s Café at Fred Segal where, according to an

onlooker, she sipped a Coke and enjoyed some lively conversation. Every so often, Bosworth hopped on her BlackBerry before returning to her conversation.

• Jessica Simpson, showing up to see rumored onetime beau Adam Levine take the stage with his band Maroon 5 at the Troubadour in West Hollywood. Simpson and her girlfriends went straight up to the balcony to check out the concert, and she sang along to just about every tune, according to an observer.

• Nicole Richie, tanning out by the pool during a casual day

with friends at the Beverly Hills Hotel. Richie ordered lunch - a grilled cheese and French fries - but the source tells us she “barely even touched them.”

• Foo Fighters frontman Dave Grohl, strolling around Barneys

New York in Beverly Hills with his daughter, Violet, 1. Sporting black

jeans, a black t-shirt and sneakers, the singer looked more like the perfect

dad than rock star, with a stuffed toy hanging out of his back pocket. Violet wore a white embroidered dress as her rocker papa kissed her head.

• In Europe for her tour, Beyoncé hosting a private

party at hot London club Paper. Looking fabulous in a ’60s halterneck dress,

the singer made her grand entrance as “Bootylicious” played - and then

headed right to the VIP area. Then, she pumped up the crowd by asking over

the microphone, “Are you having a nice time?” The singer partied with her entourage until 3:30 a.m. and danced on the tables. A partygoer told us: “It looked like a music video. When she was dancing her hair was blowing up in the wind.”

• By DIMI GAIDATZI, JENNIFER GARCIA and JESSICA HERNDON

Monday’s Couple Watch >

What happened in Vegas? Don’t ask Kate Bosworth - she can’t remember!

The 25-year-old actress cannot recall shooting her love scene with Jim Sturgess for 21, she told PEOPLE at Wednesday’s Cinema Society and Calvin Klein Jeans-sponsored screening of the film in Manhattan.

“We were both so drunk,” the Superman Returns star said. “Jim and I became such good friends, we decided to have a couple of drinks, loosen up and go for it.”

Surgess - who plays the lead in the shot-on-location casino flick, based on Ben Mezrich’s book, Bringing Down the House: The Inside Story of Six MIT Students Who Took Vegas for Millions - has similarly fuzzy recollections.

“We were on Grey Goose, I think,” said the British actor. “It was brilliant for about half and an hour. As we continued to drink … it just became sloppy and messy. I couldn’t stand up at one point.”

After the screening Wednesday, the two stars headed to SoHo’s Mercer Kitchen, where Mary-Kate Olsen, Helena Christensen and Clive Owen joined in for dinner and blackjack.

Unlike in Vegas, everyone was on their best behavior.