Event attendees are quickly becoming accustomed to using Twitter as the "must-have channel for conference back-chat" - an interactive audience-sourced dimension added to speaker presentations. Whether that's a good thing or not can be debated, but it certainly seems inevitable.
And now Google Wave is here to challenge Twitter as the backchannel of choice among early adopters. Although it will likely be some time before this becomes mainstream, here's an example (with screenshots) of how Google Wave might be used to create a crowd-sourced write-up of a conference presentation: a transcript of key points and a record of audience comments.