Yes, I bought one in May, and No I haven't had any issues with it.
Now for the fine print:
1. I am an amateur and it is winter here now, so it hasn't had much of a workout yet. I will be going to the zoo this weekend, and on the Google+ 2nd Anniversary Photo Walk next week, so I will be more familiar with it by then.
2. My serial number is 80273xx, but I don't expect that will be of any value to buyers in the US because Nikon are selling a completely different batch/series here in Oz.
3. I have a sensor cleaning kit which I have used successfully with my (much) earlier D100 and D1x, both of which I still have. I have no qualms about cleaning the D600 sensor when the job is required.