I joined up with BNI last year, and it's been pretty good for me. The people in the group have brought work to me, and referred other people to me as well. So far the ROI is 5:1.
The good thing about BNI, vs. some other networking groups, is exclusivity. You will be the only framer. And you won't find yourself swarmed with wave after wave of insurance agents and mortgage brokers. In our group, we have a massage therapist, a dentist, a chiropracter, a contractor, an accountant, a lawyer, a hypnotherapist, a guy who buys and sells cars for people, a photographer, a dog walker, and various others.
That being said, not every BNI chapter is the same. I suggest that you go to the meetings of several BNI chapters in your area, if possible, and meet as many of the people as possible. The right mix of people can make or break a group for you.