Far too much.
I never bothered to care on my clocked times. I'd guess in the neighbourhood of 1000+ hours, though.
Good, evil, boy, girl, all DLCs, cranking specific skill setups (min-maxing) and/or stat setups, full-maxing; you name it.
A good chunk of my life is forever lost to nothing but memories and ~10MB save files.
And I'm perfectly O.K. with that.
Tin Man said:
Fuckloads. Easily 150 hours plus. Nearly had all the achievements, but then when I entered the room in The Steelyard that held the last 3 ingots, my game crashed midsave and corrupted my data, never to be read again. It was hardly the first time the game screwed up on me, but terminal fuck ups are terminal.
The pain was tangible. It literally hurt me. This was about a couple of years ago now and I just can't bring myself to start that game again. I haven't bought New Vegas either, cause I hear thats even MORE buggy. Damn shame, I truly loved Fallout 3, but broken games are broken.
This is why I always create 5 save files and rotate through them (most often, for RPGs, but really for any game that allows it). It spares you that sort of grief, and has the added benefit of allowing you to backtrack in the case of missing critical elements of something (or just wanting to replay a particular stretch; I usually keep seperate saves for my more beloved moments in a games' story).
I got into this habit during the PSX-era Final Fantasies, to be honest. Multiple save files for specific boss fights and cutscenes. Needless to say, I had at least 2 memory cards per FF.