I started the p90x system about a month ago and I love it! I have been seeing huge results in a short amount of time which is great for me because I live a very busy lifestyle. Some of the workouts are a little overwhelming at first, but it's worth the effort!! Just do whatever you are comfortable with in the beginning... it's better to only do half of a workout than to struggle through it and hurt yourself.
I altered my workout by increasing my reps. and decreasing the weights (just hit "pause" and hammer out a few more reps!) so I could get the tone and not the mass.
I can't say enough good things about the diet plan either! The portions are very generous so I'm never hungry throughout the day... lots of chicken, fish, and steak and plenty of fun recipes!
If you do end up trying it, let me know what you think!!