Synchronize! makes quick work of a backup to a second hard disk, removable disk, or AppleShare server.

Check the "Master" check box under the appropriate folder, check the "Delete files and folders not in the master folder" box, uncheck "Show files to copy" in the Options menu, and check the "Start copying before Quit or Shut Down" box.

Now, run Synchronize! in the background. When you shut down your Mac, Synchronize! will automatically back up your Mac, before completing the shut down.