Indeed. If you're trying to back up your entire system, I'm afraid you'll run into some trouble. I don't know that it's impossible, but Deja Dup was designed for easily backing up a user's /home folder.
Originally Posted by NikTh
I've found a great way to pseudo-back-up my system is to use Deja Dup to back up my /home and then use the "Sync between computers..." option in the Software Center to keep track of what packages I have installed. If something happens, I can do a fresh install, install the packages I had before, and extract my /home directory, and presto! (Exception: manually installed packages take a little more work.)
Jane, stop this crazy thing!