Upgrading? Archive your old iPhone backup folders and save space

I upgraded my old iPhone 3G to a 3GS and lost about 8 gig of disk space. If you have successfully upgraded your iPhone to a new version the old backups are retained here:

$HOME/Library/Application Support/MobileSync/Backup

Look at in Finder, sort by date and then just move those folders to an external backup drive you aren't using any more. Note, you will definitely want to keep the most recent folder as that is the active backup of your iPhone. This worked for my setup, but please use caution cause these are your iPhone backups - move, don't delete!

It's worth it to get 8 gig or so back.