I've heard mixed reviews. On the negative side, the people who are the trainers tend to have differing levels of expertise and experience. It seems like some of them may not really know what they're doing. Then again, I know people that love it and find it a great way to stay in shape and meet new people. I guess it boils down to the trainer and the group ultimately. I think exercise is always a good thing, but you have to be sure you're doing it safely and, in the case of crossfit, with someone who knows what they're doing.