Today I began my third round of P90X after having completed a round of Insanity in June of 2010. So far I've lost about 20 pounds of weight, put on muscle improved my endurance and lost about 2 inches off my waist.
People ask me if P90X works. There's no magic to it. Anything you work at for an hour to an hour and a half a day, six days a week that burns calories and gets your heart rate up along with a sensible diet is going to work. The thing I love about having a program to follow is I know exactly what I'm supposed to do each day and I have something to hold me accountable (the calendar) if I don't do it. In the eight months I've been doing the programs I've only skipped one workout that I didn't make up later.