I was in BNI for about a year. It was good, but not perfect. I think the meetings have to much filler. If they were shorter and more to the point I would probably have stayed longer. Too much time spent talking about favorite hobbies and backgrounds, etc.
I would recommend joining and giving it a try. If your chapter has people from similar fields, it seems to work much better. I made some great connections and it was well worth the investment. I just couldn't do it forever! Make connections with the people in similar trades first. Plumbers, landscapers, painters, etc. will all be able to easily trade business with you. I even met a few PMs through BNI, although none were actually in the group. If there is a PM in the group, join for sure! BNI members tend to be very loyal to everyone else in the group.