A professor at Brigham Young University asked the same question. I sent the following ideas to him. Let me know what you think!

-Solicit feedback on class discussions, research you are working on, etc.
-Post interesting links to things discussed in class for further review
-Let people know about upcoming assignments and announcements
-Have them set up their profiles to link directly to Facebook or their phones so that whenever you make an announcement, they know immediately
-Offer extra credit for doing something above and beyond the class
-Start a discussion on a particular topic
-Distill key class ideas into a series of “Things to Remember” posts
-Monitor keywords using one of the Twitter mashups for trends (see http://blog.guykawasaki.com/2008/12/how-to-use-twit.html, http://blog.guykawasaki.com/2008/11/ten-tiny-apps-t.html)

Here is the link to the “Beginner’s Startup Guide” that you could send out to members of the class: http://twitter.zappos.com/start