I just got back from ETE 2009 in Philadelphia, and it was really a great conference. Andy Hunt the Pragmatic Programmer was one of the keynote speakers, as was the CTO behind the Obama on-line presence for the campaign.
I learned a lot, but something that really stood out wasn't what was in the presentations, it was what was going on between the audience. It was Twitter.
I have heard about people using Twitter at SXSW for meet-ups, or at large conferences to talk about the speaker while they were speaking, but I had not personally seen it before.
Frankly it was amazing, and I think part of that was that the organizers specifically suggested using the tag #phillyete in all of their posts. Prior to the conference there were a couple posts, but nothing worth mentioning. On the first day of the conference it all exploded.
I was reading about people stuck in traffic, getting on the plane, and otherwise in transit to the conference. I heard about spontaneous attendee created meet-ups, and who met who. I even read about who lost at the Guitar Hero competition (me).
During the talks if you watched Twitter you could see what people were saying about the speaker. Usually it was good stuff, but a few times you could see that the session wasn't what they thought it would be.
Even though the conference is over I still see chatter. Seems there is an after-conference meet-up tonight. Maybe I can make it.