I've been doing the original P90 for about a month and a half, I moved up to the second stage a couple of weeks ago. I've lost about 10 pounds since I started, but the first set didn't really push me very hard, the second set is about where I need to be. After I get "used" to these, I'll do P90X.
I still have a gym membership, I like to lift weights too, but you can get very good cardio with these vids.
First post on here, I've lost about 70lbs since I graduated college, still have about 20-30 to go, want to get in shape now mainly.