I did it, it was awesome. I just re-started again 2 weeks ago and I'm already up to lifting 15 lb dumbells. I love it. I just ordered P90X2 preorder for Christmas for SO.
I did it earlier this year and loved it. Got great results. I wish I had kept up with it after the 90 days and put some lbs back on, so will probably start up again after the holidays. Or maybe tomorrow!! haha
It was definitely the hardest workout i've ever done, but for me, the workouts made me push myself harder than I would have on my own.