I belong to several yahoo lists and the talk on two of them have lately revolved around critique groups. Whether they help or hinder or don't make any difference a'tall.
Well, I belong to two critique groups. One is a mystery group that meets at a local bookstore once a month. One chapter a month is too slow of a critique for me personally. I write faster than that. I do enjoy reading what everyone else has written, the critiques are honest and challenging, and I always come home recharged and ready to write.
The second is an online critique group made up of women who write erotic romances running the gamut of genres: Sci-fi, chick-lit, historical, suspense.
What I look for in a critque group is a sample audience. I try out my words on them, they tell me if it works or not for them, and then I go fix parts that I agree are wrong and hopefully make it better. I dont' expect everyone to like and admire every word I write. Heck, I know I write crap at times. But, I do expect them to be honest and tell me that it's crap. That whole feedback loop breaks down when no one gives an honest assessment (good or bad).
I'd say join, try one out, if it doesn't work for you, try another one.
Writing is such a lonely occupation at times that it's great to have a group of people sharing the same experience.