Here is one interesting and real-world use of Twitter by the Los Angeles Fire Department. Members of the fire department provide real-time updates of LAFD activities and operations. Anyone interested can subscribe or follow this Twitter. Imagine the uses at a college or university - we could provide updates on availability of writing or math labs or even our testing center. We could also provide registration information in real-time, such as number of seats, new sections, cancellations etc. To think of it, you could also use these tools to manage your office hours - in real-time!
Here's a great New York Times article on Pownce and co-founder Kevin Rose. Who's Kevin Rose you ask? Kevin is the 30-year old wunderkind behind hugely successful news/social networking site digg.com. Digg allows user to post links to interesting news or websites and other users to either "digg" or "bury" the article. Stories with the most diggs rise to the top, while others disappear - it's a great way to let the community filter news.
I have a few pownce invites left, email me at firstname.lastname@example.org if you'd like one - first come first served.