Exercise/Gym Bootcamps?

What do you think about the exercise or gym bootcamps many fitness trainers are offering? They're intense sessions that are meant to get you into shape fast in anywhere from a few weeks to a few months.

The thing I'm wondering about is the intensity of the bootcamps. Just as extreme diets don't work over the long term to lose weight and keep it off (for the most part), I was thinking that this would likely be the same with exercise.

Also, we're always being warned to start a new exercise program gradually and to be sure that we're doing what is right for your level. So, how can I, a 48-year-old woman, with a good BMI but not good exercise endurance, take a bootcamp type of class with a group of 20 and 30 somethings who are in better shape? Is it possible?

Have you ever done this type of extreme fitness training? I'm curious - there's one available near me and I've sent the owner some questions. I just don't know if it's something I'm ready or able to do.