I rented a D600 in Canada that had dust but it was easily blown out. The D600 that I bought also had dust. I was able to blow out 85% of it and the remainder did not show on my images at normal apertures. I just got the rest of it out with one pass of a Visible Dust wet swab.
I don't think it's huge problem in the two D600 bodies I have experienced. There has been some speculative talk on other forums about spots being oil splatter but I am quite certain that the spots I experienced are not oil.