I don't have a D800 yet -- but am seriously contemplating one. One feature that I've not seen discussed (It may well have been -- I've not been on the internet much for a while) is the "in camera HDR" function. Even Google doesn't turn up much on it, but the couple of examples I've seen from the Nikon web site seem pretty impressive.
Is this feature usable, and what kind of results are you seeing with it? Do you end up with just the merged file or do you also get the individual frames plus the merged file? How do you set it up -- through the menu? If so, can it be in "My Menu so it's a one step process?