Leopard Upgrade - What to backup?

I'm not sure about aparture, but what I did for iTunes was just drag the "iTunes" folder onto an external and then once you have Leopard drag it back into the "Music" folder. Then when you boot up iTunes everything's there, nice and preserved. Good luck!

 

Hmm I can't speak for your computer, but on mine, everything 'itunes' was stored in the music folder, which I simply copied over after doing a clean install. Then when I opened iTunes for the first time it was all there, just like before.

 

No no no.

Even if you keep your Music on a separate drive, you need to open the Music/iTunes folder on your internal drive in your home folder. The iTunes Music folder inside iTunes should be empty, but there should also be an iTunes Library, an iTunes Music Library.xml (both files) and a Album Artwork folder. Copy these. Then copy them back after you install but before your launch iTunes. The Library and Music Library.xml files contain all the library data incl. playlists, play counts, iPod sync data, stuff like that.

As for Aperture, not really sure. There are a lot of files, preferences, .plists, and other items located in the user Library folder as well as the computers Library and System folders. It is a good idea to back up those three folders as they can contain Application Support, etc. The one thing about a clean install (considering one myself) is that all your preferences, system, and per program, as well as application installations, and other minute details need to be redone from scratch depending how much you want to recreate the look and settings of your previous workspace. It may be a good idea to make a list of applications, backup installers for downloaded ones, etc. as well as making a list of anything else you can think of so that you can reorder your stuff after the install.