I have an ibook 366. For a long time I have this problem that occurs after the machine is in use from several minutes to several days. Suddenly, while changing applications or switching windows, the rendering of the menu headings and the window titles is corrupted, as though the anti-aliasing isnt working. The font in the menus themselves looks fine, and fonts in folder views and icons look fine. I almost always have IE5.0, Outlook 5, and AOL IM running at the same time, and it only seems to happen when IM is on, but I am not sure. It's getting annoying because I have to restart to make it go away, and the problem persists after months.
I have ATM Deluxe 4.6 running, but I have had the problem even when this is disabled. Also, in the Appearance control panel, I have "smooth fonts on screen larger than 12 points" checked. Whats the deal? My similarly set up Powermac never does this . . .