Let's not leave out the fun factor. Entertainment has always been at the core of the social networking experience, and as social networks become more sophisticated, there is a huge potential for having fun while socially networking.
Facebook is quickly becoming the platform of choice for casual gaming. With the ability to easily manage having a chess match with a friend even if they live halfway across the world, it is easy to see why Facebook games are so popular.
But having fun on social networks isn't limited to just games. Niche social networks can match your interests with social networking. Love movies? Try out Flixster and play the never-ending trivia game. Like music? Let Last.FM help you discover new bands similar to the music you like. A sports nut? FanIQ will let you show the world just how much you know about sports.