Now that everybody and his mother is on Facebook, is it time to look for the next big thing in social networking?

Last month, Facebook gained its 300 millionth user and turned a profit for the first time in its six-year history. Can we just Facebook forever, friend requesting until we are officially connected to everyone? One year into Facebook's unchallenged social networking domination -- three years ago this month from its availability to the general public -- and suddenly people are beginning to speculate about its demise. All social networking sites eventually die off, mutate or find a second life elsewhere, as evidenced by the ones that have come before. But why are we so eager to move on?