Purdue University is exploring a home grown program called Hotseat that integrates Facebook, Twitter, and text messaging (via a mobile device) so students can "back channel" during a class.
Back channeling has become popular recently at conferences and presentations. People use an application like Twitter to ask a question during class, and the teacher (or a speaker at a conference) can address that question during the time of the presentation. With Hotseat, students can propose questions and others can vote on the question to be addressed during the class. Regardless of the application, I think back channeling is a great way to use social media to engage your students and get instant feedback. To learn more about the program, view the video below: