P90x is a very good program because it is comprehensive. It covers resistance training, cardio training, flexibility, core stability concepts, ect...
The only problem I see with it is that is sometimes too difficult and complex for many individuals to execute properly.
So if you are experienced and dedicated it is great, but I would not suggest it for beginners.
If you would like more information and free video on fitness training you can visit my free information site:
Jason Chiero, CPT