There is a definite life cycle to social media sites. Those reaching the "too big to fail" stage are usually about to. AOL, CompuServe, MySpace, etc were all indominately massive juggernauts reaching to take over the media world - and vanished almost overnight. The sudden influx of editorial censorship in Facebook, YouTube, Twitter, etc is a clue that a large number of legitimate users (who just happen to hold differing expressions of differing views) are facing the option of leaping to another up-and-coming site. Between that, boredom with format limitations, and an otherwise growing sentiment of malaise, I'm seeing the signs that FB etc won't be with us much longer.
And no, it's not "different this time". It's the same this time.