if it happens to you its very obvious, many times it will tell you as soon as you save that there is an error saving to the hard drive. with quicksaves it doesn't flash the error warning, which has gotten me in trouble in the past. also under your list of saves (ingame and in your files) you will see the suffix 'TMP' after a corrupt save. finally, when you click on the properties of one of these 'TMP' files you will notice there are fewer files then are supposed to be there.
if you haven't experienced any problems under the new patch and you've been playing for a while than its probably nothing you need ot worry about, i've had this problem since i started playing the game.
this seems like a really great game, but i need a fix for this problem if i'm to continue playing: its just to frustrating otherwise.