I attended BNI a while back for roughly 8 months. I found it very frustrating.
Same group of people week in week out, pitching the same blurb. It got to the point where it was clear no-one was listening to the others pitch which made the meeting pointless, but people kept returning regardless as they had paid their yearly subscription.
Very little business passed around, mostly internal referrals for free services to get the groups figures for passing business around up.
There are some decent networks around, but apart from the first week when it will seem like you could do lots of business, once your in you will find it can be very clicky, with other networkers not looking to pass business your way until they know your in for the long haul - they don't want you turning up for one week, taking business then disappearing.
It takes a bit of time and commitment (more than just attending for breakfast, you need to dedicate time long after the meeting has finished) to really get anything out of it, something I didn't want to commit to in the long term, after 8 months mind.
Way up the time, commitments and cost and then see what else you could be doing. There are people that have attended these things for years, and swear by them.