I did get a D800 and I did get it serviced by Nikon. I was very reluctant, in fact it took me a while to convince myself I had a problem (mostly because I didn't want to risk Nikon screwing it up from all the horror stories).
But it went off, came back reasonably fast (I don't recall example, a few weeks), worked much better, was all handled very professionally.
It is the only thing Nikon I've ever had to get fixed; I suspect most people are in that situation, you buy it, it works, done. But my one data point was done well.
I would absolutely agree with the other suggestion - buy from someone with a no-questions return policy just in case, and test your purchase with all your lenses in real world situations (plus some contrived ones if you like) in that 30 days.