Just to list a few.
My life is so consumed by these "social networks" that sometimes I have to stop and wonder where my real-life social world went. All of this socializing through technology can't be healthy.
But it's oh-so enticing; you can ignore whoever and whatever you want while feeding your social hunger with only the things you wish to expose yourself to.
Smart networking? The wussy way out of actual human interaction? Whatever it is, it's highly entertaining and extremely useful to talk about things your friends may not care about but other people will gladly read for the sake of keeping technology alive and much too well.