The issue of comparison with previous cameras is a good point of reference. I encourage anyone with concerns to take a look at their current camera as it is today and test it for dust.
Mike Hagan (of Nikonians Academy) had a recent blog post comparing his four current camera bodies for dust. He found that the test being used revealed similar dust on the sensor in every camera body. And for those coming from DX, be sure to multiply the amount of dust by 2.5 times to reflect the larger FX sensor.
The resolution, dynamic range and high ISO performance of the D600 is truly excellent. And the updated AF system is very good. It is a very good camera and a solid entry in the Nikon lineup. There may be more dust than normal in the mirror box, but since most dust is easily dealt with using a blower, I would expect this to be a minor issue for most photographers.