Long time ICQ user (3787015), but have AIM, ICQ, Yahoo, & MSN all in use. AIM by far gets the most use of them all now. ICQ has really gone down hill although I still think it is a much better protocol (with offline messaging and all).
I use Trillian
as my program of choice. I have tried GAIM, but didn't really like it as much as Trillian for some reason. I have used Trillian since its pre-beta form and have never looked back.