I admit: the only social network I'm taking part of is LinkedIn. I don't like twitter, because I don't feel the urge to talk into the void. I don't use facebook, because I'm not looking for a date. The list goes on...
One side effect I noticed about social networks, facebook specifically, is the fact they encourage anti-social behavior. I'll explain. In the past few months two of my friends (which are not related to one another) got back from a long trip abroad, and found new jobs. Some mutual friends of mine were able to tell me the details about the pictures uploaded to facebook, and the job title of those that came back. But that's it. Nothing else. Most of them didn't consider calling or meeting and get the details about the trips or the jobs. In my opinion, this is what matter most. Seeing someone's pictures is one thing, but listening to the experience and the stories around the trip is entirely different.
So those who gets updated through somebody's profile might think they know the person in question, but in fact, they know nothing.
Other side effect is the fact some people are relying too much on those networks as the means of communication and the primary source of knowledge about those they are connected to. Others, rely on the network's updates about people's status, birthdays, couple-state (single, with a g/f or b/f, married, ...), etc. too much. No updates - no knowledge.
The sad ending of this post is the fact I don't think things are going to change for the better. We'll rely more and more on technology to do our tasks, including social tasks, and our brains will become degenerated.