Instant messaging and chat.
I like it. I feel connected and in touch. Problem: I'm in a customer service oriented industry. I can't ignore my walk-in patrons/customers to "online chat" with a friend/coworker/fellow librarian/library. I was fortunate in that I have a few young (really young) friends who were willing to help me along without making me feel ancient and way out of touch.
I'm sure there is a use for these functions in libraries. I would imagine that large library systems could and should use it extensively. It's so much faster than e-mail. You get instant response. If a patron was making an inquiry, you could IM another branch or speciality library if necessary and get a quick response.
We haven't publicized use of instant message or chat from our computer lab. I think the icon is only available when the computers are in "Administrator" mode. Most of our patrons use our computer lab for employment search, genealogy research, distance learning etc... Quite a few of our regular computer lab patrons (adult and youth) simply watch TV shows, anime or play games.