Im not sure if i should admit this here but i deleted iChat long ago and I never even used it once. I use skype to talk to my woman, who has windows vista, twice a day and I use Adium a bit as well.
I used to never use iChat. I use from time to time since Leopard came out because screen sharing allows me to do remote technical support for my tech-clueless friends without having to issue instructions and have them go "what? what File menu?"
It's good to have it around.
Of course, it makes it easier that everyone in the U.S. uses AIM.