That was me on the post yesterday (man, with all the mistakes, maybe JR is my long lost twin?)
It is seriously intense.
I think a big part of it is that if you stick to it like you should, you are looking at 7 days a week, 45 minutes-1.5 hours of exercise a day. That's a lot more exercise than even some people who go to the gym to hit the treadmills and such are accustomed to.
The pull ups from what I've read aren't just up-down-repeat, but have a lot of lateral movement as well. So even if you're just dangling there and can't go up all the way, you can still get some benefit from it.
My belt actually BROKE the other day, and a pair of pants I fit into 3 months ago I'd be lucky to get in with the aid of Crisco and a Shoe Horn. My goal now is to drop 25 pounds in two months. I think I'm going to try to contact someone on Craigslist tonight who is selling it and see if I can pick it up later this week. I don't have any weights here or a pullup bar, so that will be next on my list.
I will say that I am still just as sore today as I am yesterday, especially in my legs/hamstrings, and that was with just a single 45 minute workout.