I fell for the hype and bought a D800 from a small local dealer. I also bought a top of the line 24-70mmG, and a very good 80-200mm f/2.8D and I already had a 50mm f/1.8D as well as several lesser Nikon and Sigma lenses. I also bought a used manual focus 200-400mm AIS, and a 500mm reflex, so I had reasonably good glass to try it with.
At ISO 100-400, the DR was amazing, clearly better than anything I've seen before, and i've owned all the high end Canon bodies. However, as ISO's rose further, the noise increased faster than I thought it should, so NR was required in increasingly heavier doses.
Then, the huge file sizes took 5-10 seconds to render, and just applying a bit of NR would take my PC 30 seconds to a minute using LR 4, while it took 1-2 sec for the 5D MK III files. Since I had several hundered images taken in very low light to edit, it was painful.
Finally, after editing the first 1000 images, I'd had it. CA's from the 24-70mm were horrible and even when lens corrections and CA removal applied, they were awful. It was difficult to get sharp images without extreme care.
All the troubles for a camera that was really a studio camera optomized for low ISO's was not what I wanted. I was also put off by no affordable lens that had comparable quality to my 24-105mmL, my 135mmL, or my 100-400mm L The 200-400mm lens turned out to have focus issues, so I returned it. I could have bought all three of the Canon L's I mentioned for the price of that lens.
I sold it all, except for the mirror lens which adapts to Canon nicely, and bought a refurb 5D MK II which I like much better as a all around camera.
So my conclusion is that its a fine body, but I struggled with the lenses and lack of high quality ones to match my canon lenses, and with high ISO's where the DR is actually poorer than the canon 5D MK III.
For landscapes and studio images, it is be a great camera. If a PJ just uses jpeg and does not have to edit the images, he would like it, but the first time he sits down to edit 1000 raw images, he is going to learn something new.