I enjoyed doing instant messaging. It was fun. I did one of my friends from a previous job. The only problem, which is similar to email is that you cannot tell a persons' feelings, so the personal relationship is lacking. I have not talked to this person in years and interpreting her sarcasm or when she was being serious was difficult. If I talked with her more frequently this may not have been an issue but who knows. I would probably use instant messaging personally from time to time when my kids get other with my husband (I do not have text messaging) with setting up who needs to get who or pick up something at the store or things like that. My spouse spends 96 percent of his time on a computer for his job so this would make things a little easier.
As for the library, I think this could be awesome when relating to patrons, especially if their is a patron who is deaf. I see messaging good when doing some of our presentations or program if someone who wanted to attend the presentation/program and maybe did not have transportation. They could get on the internet (of course it would be a podcast or webcam) and the patron could add their comments in relation to what is being presented and open up the disscussion further.
Currently, our library, at least not to my knowledge is offering chat/IM, but I know our library director is trying to incorporate all these things into our library as soon as possible.