I've had the D600 for about a month now along with the 24-70 f/2.8 and the 50mm f/1.8. No dust spots yet, although I will carefully check again tonight.
Here are my impressions so far:
In terms of ergonomics, the camera fits well in my hand and isn't that different from my K20D in terms of size and weight. The build is probably one notch below that of the Pentax though. The K20D feels a bit more solid and substantial. The difference is relatively minor.
There are a TON of customizable options and the buttons are generally well laid out. However my biggest gripe is the placement of the ISO button. It's on the lower left which makes it impossible to adjust it on the go. You have to let go of the lens and push the button. My workaround is to assign the Fn button on the front of the camera (which I can reach with my right hand) to open the first option in My Custom Menu. I've set ISO as my first option so now I can adjust ISO without letting go of the lens, although I now have to look at the LCD. It's not perfect but it works. Hopefully Nikon release a firmware update that allows your to further manipulate the buttons. The custom settings are a fantastic idea. For example, my U1 setting is set to landscape mode. (manual, ISO 100, mirror lockup, etc.) No green button though.
The focus area is as small as they say. I haven't found it a hindrance although sometimes I would like to be able to focus further to the left or right. The focusing is fast and accurate though, but remember I'm coming from a K20D.
I don't do video so I can't comment on that although Nikon is supposedly releasing a firmware update that will allow you to adjust aperture while recording.
In terms of IQ what is there to say? Everything you've read is true. It is stunning what can be achieved even at high ISO.
All in all, I'm extremely pleased with my purchase. If you have any questions, feel free to ask.