Linux Planet has my 3-part series on simple backups for both single PCs and small networks, using portable USB storage devices. Learn how to nail down your device names in udev, attach your backup command to a menu icon, and schedule regular unattended backups.
Linux Backups For Real People, Part 1
http://www.linuxplanet.com/linuxplanet/tutorials/6433/1/
Linux Backups For Real People, Part 2
http://www.linuxplanet.com/linuxplanet/tutorials/6435/1/
Linux Backups For Real People, Part 3
http://www.linuxplanet.com/linuxplanet/reviews/6437/1/
Or just use USBSink (http://usbsink.sourceforge.net)
Why? What makes usbsink more special than any of the other hundreds of backup applications? Does it make it easier to do network backups? Does it schedule regular backups? I see that it's a gnome app, which for me is not a plus. why not make it universal?