I’ve seen a few posts about it but LiB goes over the use of the MeeboMe widget in libraries pretty well. One of the big benefits of such a widget is that you can include it at problem points. An OPAC search bring up zero results? Display the widget in the sidebar. It’s also anonymous and doesn’t require anyone to add you to their buddy list, providing an easy virtual reference for those who don’t use IM.
Another service I like, which would be outreach, is Qunu. It allows “experts” to sign up and tag themselves with their expertise. When someone has a problem relating to that tag they can see what experts are available and chat with them via the website. The site is based on Jabber, which is nice to see.
I’ve been thinking about a similar idea for libraries or support desks. It would be nice to have a system that allows patrons to chat with support via the website similar to above. Behind the scenes would be a server that multiple support staff would be logged into. The server then routes the incoming question to an available staff, spreading the load among users. This gives a single entry point for users but allows multiple staff to participate. There are multiple libraries for jabber for web-based languages and I think some complete web clients. The big part would be designing the routing system. It also may already exist. Another possible interface would be to list the available reference or support with some of the specialties (and their status) and allow the user to choose. Pretty much Qunu but install locally if possible. It would likely be more overhead then some libraries want to do. For those I’d recommend taking a look at the sites above.