Upload & Sell: Off
How does the D600 fit your hand?
Are the buttons located conveniently?
Do you like/use the locking mode dial and the U1, and U2?
If the D600 is doing everything you need,
get some good Pro Glass
It is a better investment than a camera body
I came from a Canon 40D, which fits in my hand very well when equipped with the battery grip. When I switched between my gripped 40D (which I can hold very steadily in my hand) and the D600 (no grip right now), My thumb feels a little cramped because of the smaller body. I would also prefer the D600 to be heavier, which helps me reduce camera shake. I played with the D800 at the store today, and at first the absence of the rotating dial was strange to me. However, after spending a little time with it, I feel it was quicker to customize settings on the D800 than the D600. I don't mind the mode dial on the D600, but I can't say I am a fan of the locking dial. As for the U1 and U2 settings- I have not used them yet, but I can see how they can come in handy.
Perhaps the biggest thought on my mind is whether I should save the $1000 (or $1300 for the D800E) and put it towards a good lens, like the 24-70 F2.8, or if it's not worth sacrificing better handling of the D800. I know I won't need to print big, so I am not sure if there will be a difference in image quality between the two cameras. As far as I can tell, the dynamic range on the D600 and D800 are very similar. On the other hand, my time spent with the D800 showed me that the autofocus is much faster, and the mirror is better damped when taking photos.