Caution: If you are about to do an 'Archive and Install' install of Jaguar, be aware that the contents of /Users/Shared is apparently also archived off. There are no apparent warnings in the installer or documentation.
The risk is that you will install the new system, check that everything works OK and then empty the 'Previous Systems' folder, thereby losing any /Users/Shared data. Quite why it is configured like this is beyond me. But it's annoying.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020916053834966