"Networked" law firms

I've been seeing more and more about these formal lawyer networks. The NYTimes had a good piece here. I'm familiar with Meritas and the International Network of Boutique Law Firms.

Who should be a member of these? Isn't it just a question of a better "vetting" vehible for referrals? I'm intriqued. I constantly grapple with how to better refer clients and receive referrals. It seems like it's mid-sized firms attempting to compete with the mega firms on an international scale.