I started my P90X routine last week. That shit's intense! It's challenging but thrilling at the same time. The difficulty lays with keeping motivated to do it everyday and not run away screaming. My body is so sore from all the workouts but already I've noticed a difference in my strength and energy level. If I can keep this up for the entire program I'll be smokin' hot by the time summer rolls around. Yay!
polyburner:
I just started a plyometrics type boot camp class myself, definitely challenging. Far better though than just going to sit at some machine for repititions.