I just got the P90X kit. I am going to start the program in a couple weeks. I am going to start on 4/1, not sure why I am waiting, just thinking starting at the beginning of the month is better for me.
I have a couple friends and some family that has done it, they have all said that it will kick your butt. The results if you stay with the program (and eat right) will be great. I don't think I will gain a lot of muscle mass, but will tone up, and get some muscle mass. My goal is to look toned for the summer, I don't want to look like a person shooting roids or anything, just good physical shape and tone.
ETA - I got the DVD's from EBay (didn't really save anything buying the DVD's on EBay, maybe $10 at the most).. I also bought the pull-up bar and resistance bands from an EBay seller named yes4all. I think I paid like $50 for both shipped (the bar and bands). I am into the kit for about $150 total (including the pull up bar and bands).