I think they leave it up to the performer. I saw Jonathan Coulton and Rachael Yamagata there recently and both times the staff was just fine with people having cameras, and mine is particularly noticeable. At Rachael Yamagata's show they asked that people not use flash, though.
This is answer is really late, but for anyone else who wants to know: they don't check bags for cameras, but they have security people walking around looking for people using them. I watched them take a girl's digital camera away, delete the photos she had taken, and then hand it back. I saw them do the same to girl with a cell phone. It doesn't seem worth the trouble unless you can bring in a small camera and shoot with a high ISO without the screen on.