I know this thread is a little older, but I have Power 90 and decided on it rather than P90X for a couple of reasons.
1. I can do 30 min. but I wasn't sure I was ready for 60 that intense of a workout
2. I can add 30 min. cardio for a full hour that I can actually do
3. Cost.....I was able to get Power 90 VHS version for less than $25 on Amazon.com. It came with all the guides, etc...
I have told myself that if I do 90 days of Power 90 I will then get P90X. I haven't done it yet!