I have owned a D700 for about 3 years and have taken about 23000 images with it. I thought long and hard about whether to buy a D600 or not. I am not a professional. I took the plunge and have had the camera about a week. I absolutely love it. There was no dust on arrival (SN 3034xxx) and it has met or exceeded everything I expected.
The one surprise was how quiet the shutter is even without using the Quiet mode. I also believe as a result of the way the shutter moves, there is less internally generated vibration which equates to sharper photos. My D700 had an MB-D10 and so was quite heavy. The slap of the mirror seemed to me to want to move the camera more than the D600 does without a grip. Maybe I am goofy, but that is the way it feels to me. I offer no scientific proof.
When I look at handheld photos I am amazed at the sharpness and vividness of color. To say I am happy with my purchase is an understatement.