Check out the other p90x thread for my thoughts on it.
The basic jist of it (my $.02) is this:
Use it to take a break from your normal routine, use it to lean out, etc. I plan to do so in Feb of '10.
The only problem I have w/ p90x is the hype. If you do ANY decent program and follow a strict diet, you will lean out. There's nothing really special about p90x other than the fact that it's all laid out for you and the planning is done. I don't buy the muscle confusion **** either. Not in 30 days anyway. If you plateau in 30 days, you're not working hard or intensely enough. Plateau's are real, but no tin the time frame p90x suggests. Just take p90x for what it is. 90 days of strict adherence to a strict diet and an exercise plan that emphasizes intensity and cardiovascular endurance. There's even a little met-con in there too. It's 7 days of non-stop working out (although I believe one of those days is Yoga/stretching or something).
You do those 90 days w/ a good diet and just about any workout program will achieve awesome results.
Like I said, the benefit is that it's all laid out for you. For that, p90x is great. And yes, some of the body weight movements are nasty and it will kick your ass.