Despite technically qualifying for membership, I always avoided mensa for many of the reasons already mentioned here. Those stereotypes are widespread and I was not immune.
But then I was invited to speak at a mensa gathering for professional reasons, and I found the group attentive, thoughtful, funny, and remarkably insightful. They asked the best questions of any audience to which I have ever presented. There were a lot of microsoft engineers present so we didn't have a lot to talk about in terms of overlapping professional interests, but they clearly grasped the nuances and complications of the work I talked about, despite having little or no prior exposure to it.
I haven't joined up or anything, but I no longer automatically denigrate or respond negatively to all mentions of mensa, either. The members I met were all good people, interesting and well adjusted and the sorts you'd expect would make good dinner party guests. Not at all the snobby weirdos you/I might have expected.