However little use Twitter has for me personally at the moment, I can see fascinating applications for library systems. Kelly D. Allen lays them out here, just in case you (or your library system - or MY library system) need convincing. (Thanks to Librarian in Black for the link)
And here's an oldie-but-goodie post from David Lee King on Twitter Explained for Librarians.
The burning question I have is "If my library system decided to use Twitter, who on earth would write the tweets??" Someone in PR? Hmm.... Someone in our "Information Technologies" department? Yikes! I like the idea of several different folks from various departments (children's services, YA services, adult services, branch library services, and more) having the responsibility for writing fun, creative, and informative tweets. "Tweet-duty" could even rotate among interested staff members.
Perhaps our new library director, Martín Gomez, will make it happen...