Here is the periodic sampling from my del.icio.us favorites list. This time I chose the tag "Backchannel."
In training and presentation settings, a backchannel is a tool (or tools) or other established process for supporting real-time conversation (generally now online) alongside live spoken remarks. Backchannels have become commonplace in many industries during conferences, classes and other learning/informational events as a way for the learners to deepen/expand their experience and learning by communicating with those around them.
From the Centre for Learning & Performance Technologies' Social Learning Academy: How to use Twitter for Social Learning - Incorporating the Twitter back channel in a presentation
From the Free Technology for Teachers blog: Five Platforms for a Classroom Back-channel Chat
From the Ruminate blog: Understanding the Backchannel