I might be more on-the-bandwagon if I had a smartphone with a data plan. Then I could read tweets while standing in line at the grocery store. But as it is I just don't have time for it.
Libraries are doing some good things with Twitter. University of Illinois -- Urbana/Champagne tweets from their Undergraduate Library with updates on services and resources. NYPL tweets intriguing quotes from books.
I do think that we need to remember who exactly uses Twitter. I've read a study (I don't remember now any citation information for it, but I've got it on my other computer -- will update) that says that a high percentage of undergraduate-age students don't tweet. So when we create Twitter services, we need to think about our audience.