My husband and I did P90X last year, starting in January. We did the full 90 days, took a break, and then did a more modified work out after that. I still use the DVDs, although I am no longer working out 6 days a week.
The results? We both lost weight, and gained tone, as well as energy. As others have said, this is serious; you are really working hard. There's no gimmick or secret, just plain old fashioned exercising. If you follow the program, AND follow the diet, you'll get results.
That being said, as a 40+ woman, I found my muscles did not recover as fast as they used to. That's why I went to a 4-5 day program after the initial round. It's also not for someone who hasn't exercised in years; you'd probably want to start with something else and work up to this.
But I would recommend it -it's a good, fun workout program.