As a followup to my last post, I wanted to mention that the new versions of Apple’s Mail (2.0.5). iTunes (6.0.2), and iPhoto (6.0) seem to be much more portable than previous versions. After reinstalling my OS, and updating the three apps to the latest versions, I was able to grab my mailboxes, libraries, preferences, and other associated files from my previous system (because I had a backup), and drag them to the corresponding locations in my new system. My mail, music, and photos were all restored to the exact state they were in on my old system.
This procedure works with a lot of applications, and can be a big time saver when you are forced to reinstall your OS.