I'm an IMer

No, actually, I am not. I sometimes use GoogleChat, but not too often. I find that I'm not well-suited to keeping up chats. Still, IM likely has a place for reference service in the future. The pros would be that you could instantly connect to the library and a library staff member to help you in your search. Obviously, getting people to ask questions of us would be a good thing. The cons have more to do with the logistics of such an operation. Since we've never done such an experiment, it would be difficult to know the demand. On top of that, there would need to be a way to conduct triage on the questions that come into the person working the IM. My guess is many of the questions would require greater searching than could be completed in the short time frame that occurs on IM. This would mean that you would need a way to transfer the work to others, who could do more in-depth research. If you had it right on the front web page, and it appeared easy to ask the questions, then you might have some luck. I'd proceed cautiously.