Kooldrew is right, it is solid. I know several people who've tried it. It is nothing miraculous in what it tries to do. It simply recommends a decent weight and nutrition program. It even allows a cheap day or meal each week (as long as you don't go completely gangbusters on that day, this is a really effective way to keep you sane each week).
I've never done it, and people can nitpick its shortcomings all day, but for most people, even some who're fairly fit as it is, if they follow its teachings with a solid effort, they'll do well. That last part is applicable to most such programs. P90X on infomercials right now I can recommend highly based on the informercials and some I know who've done it. They didnt' get much gain out of it because they slacked off shortly after starting it, but you go on lower calories with an hour of exercise/day and you're going to look better with your shirt off, period.