Am on Google IM now, firstname.lastname@example.org
Please only request to be added if we have IMed, talked in person or emailed each other in the past.
Instructions for Gnome/Gaim users: here. Google's IM is based on the open Jabber protocol which not only allows for many implementations and creative uses of IM, but in addition Jabber is an interesting protocol that can be used to route arbitrary XML messages across the internet (not necessarily IM only).
The protocol has now a big service provider with a big user base that will help realize its potential.