Not sure how reliable this source is but he basically says P90X is not good for you:
Dear Dream: What is P90X and Does P90X Really Work?*|*The Dream Lounge
Well I'll let the results of P90X speak for themselves. My wife and I finished P90X a couple of weeks ago. I lost 28 pounds and my wife lost 15 pounds. We didn't miss any of the workouts but we didn't follow the diet very well. If it wasn't for P90X that probably wouldn't have happened because my wife and I weren't working out like we should, which made these workouts perfect for us. P90X is perfect for anyone who needs a structured workout and can't do it themselves. I don't recommend P90X to people who are extremely out of shape though, because these dvds are very demanding and can be discouraging when you can't do certain workouts.