OK, today I connected an external USB drive to my powerbook. The external drive contained a clone of the hard drive of one of my other macs. Anyway, on the powerbook. I have no app installed to handle rar files, thus, every rar file has a blank icon and doesn't open with anything. However, after I attached the USB drive, suddenly the .rar files on my powerbook got a nice .rar icon and were associated with the app 'The Unarchiver'. This app is contained on my external drive: /Volumes/External/Applications/The Unarchiver.app I never even attempted to open any app on the external drive while connected to my powerbook so just how does OS X know how to associate it with .rar files? So with no external drive attached .rar files have blank icons and open with nothing, as soon as the external drive is attached the associate with the unarchiver and get it's icon! pretty smart, but how?