For those flipping through late-night infomercials, P90X may seem like just another throwaway home workout system, Not so. P90X has a major fan base — celebrities included. From plyometrics to yoga, the system stresses the idea of "muscle confusion" — basically, you're changing up your routine so much that you never plateau. It clearly works, too: Ashton Kutcher sang its praises when he got ripped for a movie role, and Pink never goes on the road without her P90X DVDs. Keep reading to find out who else in Hollywood is a member of the P90X posse.