I've had my D600 for about 12 months.

As far as 'dust' on the sensor is concerned, it comes and goes as I live in a dusty rural environment. Today's dust smelled of turkey poop as someone close by was ploughing it in. I have my D600 set to remove dust on start-up and shutdown.

However I had a couple of spots, which in my opinion, were definitely were not dust, as you could see a distinct coloured halo around them. They were only visible from about f15 and smaller when shooting against lightish backgrounds.

I did a wet clean and they have gone. Be interested to see if any more appear. My camera has been on 'holidays' for most of the last six months and only has about 3K actuation's. From what I've read the problem seems to settle down at around 5k actuation's. Fingers crossed.