was a member of BNI for about six months back in 2004.
Sorry to say, but it beats even YP as being the worst marketing decision I've ever made.
It's true that you are not given the hard sell to join up but on the other hand when you attend a meeting you get a false picture of what the real situation is.
You see everybody stand up in turn and give a little speech about their business, then they will either pass a referral for work to another member, or provide a 'testimonial' stating how impressed they are about another members business.
To an outsider, it all looks very positive.
The reality is that most of the 'referrals' are either not 'real', or trivial i.e. I had about six referrals whilst attending BNI - two of those were to clean ONE room at another chapter members home address, and the other four were to purchase a £5 bottle of spotter :

BNI is a business, and like most businesses, puts itself first.
I remember one guy who sold/services photocopiers. During the time that I was there, I don't remember him getting one meaningful referral.
He then won a contract to supply the schools in his Local Authority area, and promptly left the BNI.
The following week it was announced 'such and such has now left the BNI - due to the fact that he has received so much business from BNI'.
I dare say that there is probably a huge difference in the 'quality' of the different chapters, which might explain why peoples' opinions are so different.
But for me it was a lot of money, and time, down the drain.