It's probably not the first conference it was done but the Forum Oxford Future Tech conference was the first that I attended that made use of it: In addition to the presentations, the Twitter feed for the conference was also displayed at the front for everyone to see and contribute. And it was heavily used by me and others to comment on the presentations and to bring further ideas into the ring. I really enjoyed that. Last year, when people twittered during the conference and it was not shown it felt more of a second layer running independently from the the event itself. By bringing it out in the open the virtual dimension and physical dimension was nicely combined. In other words, a good idea 🙂