The new Sony sensor in the D800 is at first glance pretty amazing. Higher resolution, better S/N ratio, larger dynamic range, all of which are helpful ingredients. You won't see this on the web or much in prints, unless the prints are very large. Fred Miranda's review shows a large gap between the D800 and the 5DIII. I think both cameras moved in a positive direction, with Nikon making a large leap in IQ and Canon adding more pro features to a consumer body...win win. The obvious Nikon advantages are at a pixel level, but they are there and they are real. This stuff is usually cyclical and I think Canon will rise to the challenge.
Rule books are paper they will not cushion a sudden meeting of stone and metal -ekg-