Where did all of these people come from? Why does everyone think this is all new? It all just /looks/ new... and is branded "new". It's almost all fashion.
Functionally... Buzz isn't any different from Facebook isn't any different from MySpace isn't any different from Friendster isn't any different from Classmates.com. It's hard to imagine that we've all been receiving Classmates.com spam for so very long.
Twitter is just a bad implementation of IRC that scaled poorly but was marketed properly. Foursquare, however, is on to something. But they're two steps ahead of where they need to be. They are building their house on stilts, not on a foundation. I'll build their foundation for them.