I doubt Nikon will say much more or do much more based on my experience dealing with the common GPS port failure.
I appreciate everyone's dust/oil situation may be a little different:
I purchased my D600 from my local dealer in December. I just passed 1000 actuations. I do change lenses somewhat frequently and expected to see some accumulation of dust above and beyond what I was seeing during post processing.
Looking at a white source exposure at F16, yes there were probably 25 dust spots on the test image. I used the camera's built in sensor cleaning feature and then blew out the camera with a rocket blower and repeated. Much to my surprise and pleasure, only 3 spots remained visible.
My local dealer included free cleanings while Nikon was contemplating their position. I took advantage of the free cleaning in case there was oil or other contaminant or problem that I did not notice. The dealer took care of the remaining spots and provided me with before and after test images. No oil spotting was noted.
I may take advantage of the dealer's offer one more time, but absent some real problem with the camera, I'll do future cleanings myself.