I installed Linux Mint Debian for my mother, works just as you described. Once in a while I login as root and run "apt-get update && apt dist-upgrade" on the machine. That's about it. Even when her laptop broke and she needed to switch to a backup machine, I just plugged out the hard drive and put it in the new laptop. After installing wifi drivers, linux continued to run. And I'm at peace since she doesn't know the root password or even what root means :).