The New York Times on 13 April 2009 had an article about different ways Twitter is being used:

http://www.nytimes.com/2009/04/14/technology/internet/14twitter.html

They note how it is picking up steam in the corporate world for allowing companies to quickly keep in touch with their customer base. But some other surprising uses have appeared, such as real-time monitoring of when a fetus kicks Mom's tummy, or for surgeons communicating with residents during brain surgery. Yikes!

The remote sensor-based tweets a la Kickbee seems like an area with some useful potential. The article talks about the automatic production of tweets, but there could also be automatic processing of tweets at the receiving end too. The message size would limit the amount of semantic markup you might want to use to automate processing of the incoming tweets, but I guess it could be compressed prior to sending. It would also be possible to send a long message that spans multiple tweets, or just allow for larger message size.