I can't imagine how this is possible. I played NV yesterday for about four hours. I load up today, and somehow my quicksave is now the quicksave I saved around the 2ish hour mark. I must have quicksaved 20 times since then.

WTF?

EDIT:
I recently discovered this: http://forums.steampowered.com/forums/showthread.php?t=1522475

There are about 15 threads why it does this - it is a known issue. There are also some workarounds.

assuming i understand this correctly the easiest thing to do is to only use quick save while in game, like in case you die, but if your going to shut the game down then you need to do a regular save (not a quick save). if your game crashes then goto the quicksave in the steam folder and delete it. does that sound about right.