I just installed Mac OS X 10.4 Tiger on my desktop.
After the install, I logged in and the Finder went into an endless cycle of crashing :(
Eventually (as I was attempting to disable various things to narrow down the cause) I got an error from ATSServer complaining about a corrupt font.
Of course, the message made it seem like things would be 'ok' after a logout-login (which they weren't).
I eventually determined that I must just have a corrupt font cache (which I've never had problems with on Mac OS X before, but I've seen reports on the web about other people having problems).
A quick rm /Library/Caches/com.apple.ATS/501/* followed by logout-login seems to have fixed things.
I laugh whenever I have a problem with ATS since an ATS engineer once pointedly ignored me for an extended period of time when I visited UofM to talk to the Apple recruiters (everyone else there was very nice).
Update: It figures that I would start having problems again after a few hours. Finder kept repeatedly crashing (this time more rapidly than before) and other apps were having intermittent problems (having Finder stuck in a crash cycle and also having Terminal crash is 'fun').
I ended up doing an archive and install and things seem to be 'ok' now.
I would rather have known what was causing the problem, but it was easy enough to just fix things that way (and I need to get 'real' work done too).