After seeing the P90x infomercial over and over again, I ordered it. I was excited to get the dvds and start working out again. Over all, I like the system. I will warn you: IT IS HARD. I am a 22 year old male that is in descent shape, and I can't do the workouts all the way through.
The big plus to the P90x program, is that you see the people on your tv all of whom are in great shape suffering as you are:) That is really motivating.
The P90x program will make you crazy strong. I felt considerably stronger by the end of the first week. I also felt better health wise.
If you are in reasonably good shape, but want more give P90X a try. If you follow the program, you will get awesome informercial type results. They meal guide is also great. It is very easy to follow and actually has good recipes. If you get the P90x system I suggest getting dumb bells rather than the workout bands. It is more expensive, but you can keep up much easier.