Kent Beck mentioned recently that he can't think of a situation for which Google Wave is indispensable. Jason Huggins left this amazing comment on Beck's blog post. Wave could very well be indispensable for implementing a "backchannel".
A backchannel is a multi-user space for commenting on some action being shared by everyone on the channel, whether it be listening to a speaker at a conference or attending a meeting during which people take turns speaking. A backchannel is perhaps most commonly implemented on IRC, but any reasonably robust multi-user messaging tool will serve.
But it's not only conference attendees that need a backchannel. Coming up I have a couple of articles recommending required communications channels for distributed teams and very large teams, wherein I strongly recommend having a backchannel during team meetings. It really is a critical core practice for distributed teams.
But even given an IRC backchannel, a lot of information gets lost during the interaction. The chat goes by very quickly, and it is impossible to type all the ideas one has into the backchannel (along with everyone else) fast enough or efficiently enough to capture everything that everyone thinks. Running a backchannel on a wiki is far too inefficient to be effective.
But Wave changes that. Not only can multiple users all contribute to the backchannel at once in real time; but after the meeting or the presentation, Wave provides a persistent, shareable, editable artifact that captured at least the basic premises of everyone's thoughts at the time. Any valuable aspects of this artifact may be edited and enhanced and otherwise manipulated after the fact.
I really want to try this out soon.