A while back I found that iBook was inexplicably grinding to a crawl. After much ado, I traced the problem to AIM, consistently usurping 67-81% of my CPU -- even when standing dead-still. I fired AIM, replacing it with Fire, a kitchen-sink (AIM, ICQ, MSN, Yahoo!, Jabber, IRC) IM client. But Fire had its own little irritations, not the least of which was inconsistently causing my sound to disappear; Entourage couldn't chime it's little blliiinng when I had mail and Fire itself no longer poo'deep'd when I had an incoming IM. So I packed up my buddies and moved into Adium, a nice clean AIM-alike with optional combo-window holding my buddy list and tabbed individual conversation windows. Once you replace it's hideous sound-effects with those you know and love from AIM (a setting -- there are many useful settings), I recommend you try the combo window and enjoy!