A very useful diagram, that I can’t actually track down the original creator of this, as Wisdump seems to have gone off line.
It demonstrates nicely some of the features that were discussed in the recent Poke 1.0 Symposium. Facebook is at the meteroic growth rise – how much is viral spread and how much the profile it has in the press, I’m not quite sure; no doubt a bit of both.
There’s also a very similar one specifically for twitter – also at the meteoric growth stage. (“Cogdogblog” attributed the design to Kathy Sierra.)