Local Chambers of Commerce used to be the best examples for this phenomenon however the luster of Chambers of Commerce and the number of active CoC members has dwindled.
I am sure part of that decline has to do with the growth of social media and a perception that there is no need.
The problems with Chambers of Commerce and Business Networking initiatives has more to do with instant gratification. CoC simply does not yield the instat gratification in terms of increased customer traffic because you typically cannot measure word of mouth referrals.
Business Networking does work and there used to be a Chamber of Commerce member discount, which gives a way to track the effectiveness by tracking the discounts.
We at O4BO.com do a combination of business networking events, our regional and national business listing sites as well as an active social media management service combined to help our subscribers grow.