NYU's Bobst library offers IM reference, though MSN messenger, yahoo, AOL (and maybe some others). Lots of academic libraries do this, and we're considering offering IM reference where I work. I've used chat support for our cable modem at home, and I've used my public library's chat (Question Point).
Yesterday, however, was the first time I've ever used IM chat as a patron (as an NYU student). I love it. So much so, I'm really tempted to turn into "one of those patrons" who other librarians blog about after the reference interaction.
I was looking for two articles that we didn't have in any databases where I work, and I couldn't find them in NYU databases either (turns out one of them I should have figured out on my own, and the other I'd need to inter-library loan). But, besides the answer to my question, I got a lot out of the experience.
1) I now have NYUBobst on my buddy list. Not only do I not need to visit the library in person, I don't even need to go to the website to ask a library question. I love this.
2) They're my friend. They log in, they log out. The librarian is like a real person, and they're my buddy. Even when I'm not doing library work, I see their status and know NYU's Bobst library is there to help me. This is where the "bad" library patron comes in bc I just want to chat with them sometimes... even when I don't really have a question, just bc they're online (maybe I shouldn't admit this online-- how many of you now think I really need to get a life?)
3) I can ask them questions from my phone with IM. If I have a really pressing reference question, as long as I have my phone around, I have a reference librarian! I guess that's true with telephone reference also, but for whatever reason, IM reference seems easier.
And finally... for whatever reason, I really value this service. I mean, I am a reference librarian. I'm constantly surrounded by librarians. It's not like reference service is a scarcity in my life. Yet somehow, just by virtue of it offered through IM, it's a huge extra value.