As I remember many years ago, most people who frequented online message boards/MMOs that I'd come in contact with were fond of using MSN Messenger (also known as Windows Live). As it turns out, that service is now dead/defunct.
I've been on the hunt for a new IM client ever since WLM kicked the bucket. What has everyone switched to pending Messenger's demise? Skype?
The Skype client itself is pretty horrible.