In related news for the first time ever, LinkedIn trumped Facebook in a survey about which social networks people care about. http://www.bnet.com/blog/business-research/linkedin-trumps-f... Apparently helping get you sucked in to Farmville is not as valuable to people as helping you get a job and stay connected with what is happening with old co-workers. Go figure.
I'm not sure you could call LinkedIn a social network. It can be nice to find out about an old friend, but most of it is pure business. So I'm not surprised about the survey.
So it's a social network and I think it is more pure and valuable than the Facebook graph since on LinkedIn you only want a thousand connections if you're an HR person, not because you need friends for Zynga games, so most people on LinkedIn have between 10-200 connections representing old colleagues.