I have printed exhibitions from people using the D7000, and I was very impressed by the image quality. It is an exceptionally good DSLR! I am sure the D800 will be even more excellent if you pair it with the right lenses. That said, I also use an S2 and have printed large (1m+) prints from it. The S2 is so far beyond any camera I have ever used or printed from that it is quite staggering. I say this as a custom printer who makes prints from many different cameras on a daily basis. Everyone knows the lenses in the S2 are spectacularly good, but it is not just that -- having the whole system built from the ground up to accommodate 40mp+ is a tremendous advantage. The precision needed to extract the most out of this much resolution is extremely high, in everything from the body frame, focusing screen, mounting hardware, AF sensors and motors... Based on my experience with Nikon's modern zooms and the D3, frankly I think it is beyond the capability of Nikon's current lenses and manufacturing tolerance. We'll see. This is not to say you won't get very good files, but a real 36 MP on most shots? I sincerely doubt it. Don't even think of mounting anything on it other than Nikon's absolute cream of the crop, as even those are going to be a stretch.
But, I will be considered biased since I am an S2 owner. Suffice to say, I really don't care! The S2 is so good that other (digital) cameras don't even really register on my radar anymore.