It's been a long time... I'd like to bring to your attention an IM client that took me by surprise. Digsby is something more than just an IM client, its a powerhouse. Supports all of the popular protocols and updates to social networks (Facebook and MySpace). The GUI and features are so well designed, notifications are great and flexibility is there. I've tried AIM, MSN, Pidgin, Kopete, Trillian but none come close to Digsby, so far only a Windows client available but there will be a Linux and OSX versions available too.
Currently in private beta, after downloading the client enter code "lifehacker" to use Digsby.