I have the complete set. I've started it after a good year of sheer laziness, and I'll admit it was pretty tough. My schedule was fairly whack at the time, so I never finished. You don't want to slack or skip sessions.
If you want something that isn't just a power-rush and is easier to squeeze into a busy schedule, I'd suggest Shaun T's Insanity program. It's a little lengthier, but there's no requirements, such as weight sets and workout equipment; you just need a room where you can breathe and move around freely.
If you do decide P90X, good luck. Don't pussy out.