> If twitter disappeared, 5 copycat sites/apps would emerge from the ashes overnight.

5 is not necessarily a problem. 1 is a problem. :-)

It's not easy to reach "critical mass" though. Many social networks have tried and failed. Certainly the Twitter alternatives (e.g., App Dot Net) tried and failed. And hopefully we've all learned some lessons from Twitter and won't make the same mistakes again.

Or if we did make the same mistakes again, then humanity is truly doomed, and there's nothing we can do to stop it...