Just got done last week with my first 9- days of P90x. Like mentioned before, diet is very important. I'm 18, so I tried to do as well as I could following the diet plan, but of course there were some slip ups. I lost 14 lbs, and gained a lot of muscle. Started out being able to do 1 or 2 good pull ups, now I can rep 10. Went from 18% Body fat to 11.5%. I had a big of chub, now I can feel and sometimes see a six pack. I will continue doing the AB ripper X routine every other day, and eating healthy until the summer. Then I plan on doing Power 90 X.
Best part is, if you have space in your house, all I needed was 15, 25, 35, and a 50lb dumbbell. You can find torrents of the program, and if you stick to it I guarantee you will love the results.