Paul Gilster writes about the problem of audiences at events with Wi-Fi access: The not-so-silent clacking of keys provides a sensory backdrop much like a white-noise generator. You speak, and a constant barrage of tippity tap tap clack clickety clack echoes in the background. It's not symmetrical: at times, people listen and the typing stops. Other times, one lone typer hammers away--is he or she blogging what you're saying or playing Doom? The sounds rises and falls randomly in different parts of the room.
Interestingly, he talks about the second level of communication being a basement meeting, but I think he hasn't seen an O'Reilly conference in action. At Emerging Technology in April, there were always several simultaneous channels: it was more like instant analysis and commentary of a live event. People would blog and post; using IM, including IRC channels; use SubEthaEdit (ne Hydra) for Mac OS X Rendezvous collaborative note taking; use some of the unique services for discussion or note posting. [via Smart Mobs]