I was impressed by how the DevLearn 08 organizers were using the TwitterCamp application to gather tweets (Twitter messages and updates posted by the conference attendees) in one appealing visual interface.
Here is a link to the application which was created by Daniel Dura for ApolloCamp 07 and is being open sourced. The visual interface of the application can be customized to your needs, which is what DevLearn organizers did.
This is a great way of getting an audience to interact, for instance, in a real-time manner, where all their impressions are registered in s central and visual location.
The application can also be easily installed on any local machine that has the (free) Adobe Air plugin installed.
I see this being used also as a simple audience response system or interactive story telling…