Got my D600 from BH yesterday. SN 3038nnn. It was filthy inside. Obviously never opened; still factory packed. Took off the body cover and the mirror had 30-50 bits of dust, and a (small) finger print smudge on it. So I spent 45 minutes cleaning things. Then I ran off 50 shots with the camera pointed down, and checked the lens for dust.
Then I took the usual "blank wall" image (actually some matte board) at f16, and checked it out. There were spots everywhere, some quite large.
Removed the lens; locked up the mirror and used a bulb to blow off the CCD and environs. Took another shot.
Down to two spots now. No movement between shots, so I suspect that we may be seeing -both- lubrication and dust.
I can say with absolute certainty however that the camera did not last see a clean room. I used to be a Nikon dealer (a million years ago) and I have never seen such a sloppy-looking mess inside a new camera.
My experience could be unique, of course, but in conjunction with others here and elsewhere, I'd suggest you spend some loving-care time with your D600 before ever taking that first shot!