Ryan Eby just invited me to join the Ann Arbor District Library twitter feed:
He promises event notifications and other newsworthy stuff.
Once upon a time I built a "superpatronbot" that searched the AADL catalog via a Jabber bot - quite reasonably you could build one of these upon Twitter's direct message listings. Useful? Perhaps, especially if I could link a Twitter account to my library card and then be able to twitter
d aadl reserve anatomy of a murder dvd
and have it do a hold on it for me (or return some disambiguator if there were multiple choices).
(Reminder - Library Camp 2008 at the AADL, March 20 2008.)