Here is (entirely anecdotal) year-over-year growth in Web 2.0 conference attendance:
2004: 400–ish (from foggy memory)
2005: 900–ish (according to the nice woman who registered me)
Someone at O’Reilly can correct me if I have these figures badly wrong, but assuming I’m close, and recognizing that O’Reilly capped attendance this year in the face of high demand, this is remarkable stuff. Fairly bubble-ish enthusiasm, one might almost say.
As an aside, I’m also noticing waaay more suits and way more blue-shirt-and-khaki sorts than I’ve ever seen at an O’Reilly conference.