About 4,500 the last time I checked. I thought that was a lot and was wondering what that says about my sanity, so thank you all for showing me I'm not alone. :D
It would be quite a bit less, however, if not for my machinima series. Shooting takes about 20 hours per episode, and I now have 80 episodes, so ...
80x20 = 1,600
4,500-1,600 = 2,900
... when you put it like that, I've only "really" played for 2,900 hours. That's still much more than I have played any other game, though, because in second place is the Mass Effect trilogy with "only" 770 hours.