Britney Spears just started her Piece of Me two-year residency at Planet Hollywood in Las Vegas on Friday, yet a bunch of celeb friends have already shown up, kick starting her new year with a new show.

If you're thinking about heading to the Sin City show, you're in good company. Here are some A-listers who have checked out Brit in action so far.

Miley Cyrus
Miley came ready to dance when she attended opening night, and the video of her going wild in the front row has gone viral.

Lance Bass
The former N'SYNC member hit up Planet Hollywood with the dirtiest of intentions. Getting the VIP treatment, Bass was able to get onstage... as long as he crawled there. Brit walked him like a dog in some sort of kinky, ball 'n gag bit.

Paris and Nicky Hilton
The heiresses also turned up in Vegas on Monday night. And Paris got to meet a very special fan.

Selena Gomez and Sia
Singer/songwriter Sia took Selena Gomez on a date to check out one of Selena's biggest idols. After modeling her Stars Dance tour after Britney Jean herself, we could only imagine her excitement.

Adam Lambert
Adam Lambert was at opening night, hanging out with people like Selena Gomez and Katy Perry and then posting a star-studded pic.

Mario Lopez
Supposedly, Mario Lopez, who's interviewed Britney before on "Extra," got pulled onstage too.

Katy Perry
Katy Perry attended the show opening and has been waking up in Vegas ever since. She got a shout-out from Stevie Nicks at Monday night's Fleetwood Mac concert.

Celine Dion
Celine Dion is pretty much the queen of Vegas. She has had two three-year residencies in the past and has just started a third series, with dates until next August. With Dion supporting her with a big bouquet of roses, Britney has three shows already under her belt. So... just a few more to go.