Forgive the rambling nature of this post, but there are few things that make me spout more jibberish that a strong opinion.
Except for a couple of sites which exist solely because they are social networks and always have been, I’d say that most sites out there are trying to grow social networks for all the wrong reasons.
Most sites that are implementing social networks are doing so because they wish to go viral and grow their user base (which I think is a fundamental misunderstanding since sites don’t go viral, content does). Rarely is it because it provides a significantly better user experience for their customers. There are lots of benefits that could be had with a social graph that don’t require inviting (read pestering) friends as StumbleUpon demonstrates, but since they don’t improve a sites uptake they are rarely executed.
Anyone who’s suffered through Facebook’s latest incarnation will get a feel for what I’m talking about. Facebook apps are almost entirely terrible. I’ve yet to meet anyone who doesn’t wish there was a way of disabling the apps completely. Rare is the application that uses the social graph in a way that makes it better than its old school equivalent. I can’t possibly be the only one who clicks “Skip” when it asks me to notify my friends about my latest victory at some pointless game.
That’s not to say that I don’t like social networks when done right, it’s just that I see a lot of value going untapped because it’s more about virality than providing value to users.
One whole class of social applications that’s completely under represented is one that mines the social graph (relationships between users and their relationships to content) but doesn’t actually force it’s users to interact with other users. StumbleUpon, the site I mentioned earlier, does it perfectly, though recently it seems that they’re pushing the social part of it further. There was a time when you could use it without even being aware that it was a social network. You’d just happily click the button and get your digital pellet.
I think it’ll be a long while before this becomes a dominant approach to improving web apps since it doesn’t lend itself to going viral, but honestly, I think it’s the only one that won’t piss off most people tired of getting bitten by zombies, or getting an invite to yet another social network.
Rant over.
If you read this far… what’s wrong with you? 
General rant, Social Networking
