I have been using Meebo for the last year as a great way to IM despite the many different computers that I work on during the day. The great thing about Sun is you are not tied to the machine and I can move from building to building, campus to campus and log-in to my Sun Ray and get up and running. Meebo provides an IM platform that is not tied to a client but can be accessed via a browser allowing me to IM whether at Sun, on my laptop or from home. A lot of people have been using the tool as well as you can see from their version of a user map.
Another thing that is great about Meebo is the use of blogs to communicate with their customers. In the last post announcing release 24: meebo rooms which is a great concept which is analagous to channels in youtube. You can see all the great photos before you sign-up at their flikr site.