Originally Posted by Zloth 
Also, check your save game directory every couple of nights. This game makes a LOT of auto-save files and, after several hours of play, the save files get huge. They can fill up your hard drive fast.
The auto-save feature only takes up 4 save slots that it continuously re-uses. What can fill up you hard drive is making lots of quicksaves, those just create new save slots every time.