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.