It sounds really impressive, and at US$3K, it's not a bad deal, so I would think groups like landscape photographers would be very interested. It might be OK for some wedding stuff, too, but I wonder about its high-ISO capability, and I think it's too slow for most action work (although with the added grip it can do 6fps). I'll bet you can print some nice looking poster-sized stuff from it!
Interestingly, for performance shooting, both Nikon and Canon have essentially reduced the megapixels in those cameras. The Nikon D4, announced shortly before the D800, is 16MP, while the Canon 1Dx is 18MP. The Canon is replacing their 22MP 1Ds Mk. III *and* their 16MP 1D Mk IV. A lot of people are not happy about the loss of the 1D Mk. IV's 1.3 crop, so it's an interesting decision.
No single drop of rain feels it is responsible for the flood.
From my point of view, the massive increase in MP makes quite a big problem in terms of work-flow and computer power and storage requirements, which may reduce the number of people likely to buy it. After spending 3kUSD on a new camera, not many people really want to spend another grand on computer and storage upgrades. Something like 75mb per RAW file, or ~110 for a .TIFF.
Personally I'm pretty happy with my D7000 and its handy crop factor. Those who need the D800 know who they are, but people who were waiting out for it now need to ask themselves whether they can handle all that additional information
I have been waiting for the D800 for a while, so the price on the D700 could come down. Even better, this spring there should be some grade 9 dentist/pre-owned D700s dropped on the market by guys who chase the Megapixel god.