In the last months, my Mac OS X Cube started to hang when switching between windows, moving windows or clicking on buttons. After a lot of frustration, I found the reason for this -- I had 600 files on my Desktop, from Safari downloads primarily. I removed the icons and my Cube is blazingly fast again. BTW, I also changed the download directory from the Desktop to somewhere else in Safari's prefs to prevent this from happening again...
[robg adds: 600?? Wow.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031023075816736