syncOtunes synchronizes your iTunes libraries
Has a PC version too ...
syncOtunes
* You have two Mac's...
* You have two iTunes libraries...
* You never have all your songs on each Mac...
syncOtunes synchronizes your iTunes libraries
* select the iTunes library file from your first Mac.
* open the iTunes library of your second Mac through a network share.
* syncOtunes compares the songlistes and creates a folder for each of your Mac's, containing the missing song files.
* import that folder into iTunes with an applescript, not needed files are automatically trashed, and you're done.