The Idea is,

to make an Easy GUI Backup with extern Data of Disk or USB -Sticks.

You put the extern drive in and you will be ask. You want to use the drive as Timemaschine Backup. The customer can say yes or no.

The Backup will be based auf rdiff or other opensource software in the Backend.

The sofware will be make an realtime backup.
If some files will be changes the software get an Informationen from the filesystem or an deamon, and backup the file automatiklie of the USB- Drive.

If the costumer need the file out of the Backup they can click of the Timemaschine and can browser like the Apple Software Timemaschine.

http://www.apple.com/macosx/features/timemachine.html
(Like Apple Timemaschine)

in the Next Step the Softwar can Browser in any Gnome Applikation. Like Timemaschine from Apple in MAIL and Calander and other Software.

I think that is the Best Backup Idea.
It´s easy, GUI Based, Quick and uncomplicated because the user don´t do anythin.

In the next step, you can Implemate an migration tool, from one pc to an other. An the posibility to Restore by the Installation Prozess. (If the Disk is Broken or so)

Sorry, my english is not so good:-) I hope you understood. :-)