More than a fad for some - but not everyone
I know a number of people who use social media - Facebook, mostly - to communicate with a large number of people with whom they have real relationships, and couldn't stay in touch with on a one-to-one basis (ie by phone or single-recipient email), because there's just not enough time in the day. Facebook is fairly good for that sort of thing.
But personally I have little use for any of it either. I have a Facebook account, but only so that my friends can include me on event announcements and the like. I have a Twitter account, but I only use it to read my wife's tweets, so I know how her day is going (particularly when she's away on business). (I've never sent a single tweet myself, but I have three dozen or so "followers". I don't know if that's funny or sad.)
I have seen some useful applications that use Twitter as part of their workflow, both as an alternative to RSS for notifications to multiple users, and as a command channel. So there's that, for what it's worth.
I have a Google+ account, because a bunch of people sent me invites and it took no effort to accept, but I've never used it, and I can't see why I ever would.