I have an idea on the potential of bumptop photo galleries. Get a facebook app and with some of the facebook API's maybe you could potentially link certain galleries of you or (if the user allows you) of your friends. This might allow for more personalization of the desktop without having to have your pictures actually on your computer.
Also possibly linking it to the Apple's mobile me or flikr might create a better desktop experience while still allowing the user to be more online oriented.