M.M.
I have a friend that's done it, and he was in really good shape to begin with.
he said the warm up had him sucking air!
He gave it up after the first round of the program. He wasn't getting the results that he wanted without having some kind of weights.
I haven't tried it. I'm starting more of the tabata style training now, to see what that adds to my fitness regime. I find that the older I get, the more results I get from weight lifting (heavy...10-20 lbs for shoulders, biceps, etc...) than I do from cardio.
Tabata is a complete cardio working in 4 minutes. I did my first one the other day, and it kicked my butt...for free. :)