Just bought the...
Have had the D600 for one week (on evaluation).
I find the grip not quite right (compared to my D300, though much better than mt D5100). Also find the 4-way controller a bit too small and too high and a bit sharp edged. Neither is a deciding issue though.
The Iso button is in an unusual place (and has been complained about in the DP review) but it seems easy to find by touch, as it is on the very bottom.
I am seeing some dust (after 1000 actuations). Only really noticeable at F22+ at 1X mag. I am not sure the dust removal system works as well on FF as DX.
The high iso performance is probably more than one stop better than the D5100 (which has same sensor as D7000).
AF in low light seems a bit worse than the D300 and D5100, though it seems to work fine on city streets at night.
The kit lens is pretty good - at least as good as the 16-85 on the DX.