I haven't had a lot of luck with writer's circles in the past. My first one, which I joined in college, was a serious disaster.
At the time I joined it, I was dabbling with a science-fiction piece based on a dream I'd had. It wasn't the kind of thing I usually write - I fully acknowledged at the beginning of the workshop that this was not my genre of choice and that it was only a thought experiment. Still, my fellow writers (maybe because I'd admitted to being shaky in the sci-fi genre) tore my story to pieces, leaving constructive criticism by the wayside and going for the personal attacks instead (as in: "This has been done a thousand times!" "This is the worst sci-fi I've read in a long time.")
I was fully aware that the story had problems. The science didn't make sense. The timeline was a little shaky. The idea was based on a dream and it showed -- it made sense as you were reading but once you stopped to think about it you were lost.
The issue I took was that none of the feedback I got from my writing circle was helpful. Most of it was downright insulting. Rather than get feedback from a group of writers (who mostly wrote sci-fi) as to how to improve my little experiment, I was told to scrap this project and start something else -- I was clearly never going to be good at writing sci-fi, so why was I bothering?
I'd like to say that I never went back after that first meeting, but ever the optimist, I returned and got to critique some truly terrible stories. I say that now, but I really tried at the time to stick to constructive criticism.
I gave up after a few weeks because I felt like no one was interested in getting better or supporting one another. In my mind constructive criticism is the key to a successful writing group. If something is wrong with what I'm working on, I absolutely want to hear about it, but I want that feedback to come in a way that helps me to improve my craft.
The purpose of any writing group should be to support one another and hone your craft, not tear each other down and discourage our peers from experimentation. We writers are sensitive creatures after all.
Have you had terrible experiences with writing groups? Great experiences? Tell us about them in the comments.