Gated communities and networks are not necessarily bad, especially those that are related to business activities. The need for some type of membership process can be influenced by the context of the environment and expectations of participants (e.g., nature of conversations, type of information sharing, confidentiality needs). I'm not sure I would label it as a backlash per se (to public social network sites), although there are sites that arguably have inappropriate walls around them.
This trend might make for a great spoof of those Capital One commercials - in this case, "Who's in your network?"... but I'm pretty sure you would not find any of those characters in any of these social network sites:
Are you on the digital A-list? It's no longer enough to get invited to exclusive conferences or be asked to join professional organizations—many movers and shakers are taking their hobnobbing online, where a new crop of social networks aim to keep out the riff-raff by demanding credentials at the virtual door. As MySpace (NWS), LinkedIn, and Facebook have expanded to people of all ages, classes, and affiliations, there's a backlash against the open culture of social networking. Walls are going up. The scene is more velvet-roped club, not open-mic night. These three gated sites are among those with tough membership requirements and, presumably, more elite social networking.