I have a Pro photographer Client who managed to blow up both his daily backup to an internal drive AND his monthly to an External.
Just after he Associated all .exe files to Photoshop CS5, and some other ... ahhhh ... "interesting" things he did. (You wouldn't believe ...) Some people should not be let near anything more complex than a toaster.
The good news? He was using Carbonite and was able to recover it all.
The bad news? IT TOOK 13 DAYS! I think his IPS throttled him after the first day.
Not exactly the BEST plan for backing up large amounts of data. Might be OK for Mom's computer, as long as she's not a photographer or into scrap-booking! LOL!