I enjoyed co-presenting about "Google's Experiments with MOOCs" with Phil Wagner at the ASTD conference two weeks ago. We had the luxury of being in the first concurrent session slot, so we had a lively, engaged audience. Folks started appearing in the room 45 minutes before our presentation, while we were scrambling to find a projector dongle (note to self: always bring a firewire to serial cable).
We had a total of about 220 attendees, which filled the room with standing room only. The last time I presented at ASTD (2010), I was placed in a cavernous room that seated 3,000. While flattering, only about 500 people attended the session, which seemed like a waste. It was much better to have a full room. I loved hearing folks' questions and having great follow-up conversations with attendees afterwards.
What I don't understand about training conference presentations is that we know that lectures don't work best. Why do we spend so much time lecturing and sitting in lectures? I am guilty of delivering lectures at conferences, with small breaks for discussion and question/answer sessions. When I created a very hands-on session at the last ASTD conference, about half the people walked out of the room when it was time for the live activity. I admit, when I'm attending a conference, I often just want to sit and listen, too.