Jan. 24, 2007 | 01:30 PM EST

Caught in the Act: Who's Hanging at Sundance?

Justin Timberlake Photo by: Splash News
Caught in the Act: Who's Hanging at Sundance? | Justin Timberlake
Lance! Mandy Moore! Justin & ... His mom? Check out who's been partying in the Park City, Utah, snow:

Justin Timberlake, toasting his mom, Lynn Harless, for her 46th birthday at a dinner party he arranged in her honor at Shag in the Snow (the Sundance version of L.A. Club Shag). The singer/actor (in town to promote his film Black Snake Moan) led 15 guests in a chorus of "Happy Birthday." "You could hear him singing the loudest," says an onlooker. Timberlake also presented his mom with beauty products from Desert Essence Organics, and arranged for her to be pampered at their spa. "He just seemed happy to be with his mom and do all of that for her," says the observer.

Mandy Moore, performing five songs from her upcoming CD Wild Hope (due in May) at a party thrown by Jane magazine. "They're all so much of my heart and soul," she tells PEOPLE of the self-penned songs. (For more Moore, check out our news story here.)

Bono, enjoying a leisurely lunch of cheese ravioli and Chardonnay with two friends at the 412 Bistro on Main Street. "He was one of the best guests I've ever waited on," says his server Jackie Cooper. "It was cool – he was nice." And yes, Cooper says he left a generous tip.

Lance Bass, trying his luck at the tables at the DoylesRoom.com celebrity poker tournament, held at the 5W Mansion. Bass played against Danny Masterson, Nick Cannon and the World Series of Poker champ Jamie Gold, – but all were beat by SAG President Alan Rosenberg.

Jamie-Lynn Sigler and boyfriend Scott Sartiano, dodging an awkward run-in with her ex-husband AJ DiScala at Aerie. Immediately after DiScala made eye contact – his ex and her new beau were the only other people in the store – he left, without saying hello, an onlooker says.

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