P90X has great workouts, but they have a lot of stuff requiring weights/bands. If you don't have that stuff already, or aren't going to do the workouts at a gym, I don't really recommend them unless you can grab them a la carte (Plyo, Yoga, Kempo, and Cardio will be what you should get then).
They are solid workouts, and what Shaf said is the truth - DVD in, brain off.
"Use what talents you possess: the woods would be very silent if no birds sang there except those that sang best." —Henry Van Dyke