Roland Piquepaille writes about whether or not social networking sites can be useful. He points to an American Reporter article that focuses on this topic as well, but which also relates it to web services. It's an interesting read and although no real answers are given it touches upon many trends and issues that are shaping our online/offline future.
"These criticism apply to social networks they way they're currently implemented. Because viral marketing and new media have an excellent possibility of becoming important social movements, I think online social networks will grow in importance, and at some point somebody will make one that works. We can also move to yet another stage where we statistically measure our network and learn from aggregate facts about the people we know. There's plenty there for a century of innovation."