I carefully compared the D800 sample photos from Russia, and at high ISO settings, it is not any better than the 4 year old Canon 5D2. Under normal circumstances, one should not even need to perform such a comparison.
5D2's success was high MP with good high ISO noise. Nikon's D800 achieved the first part but ignored the second part. I was expecting D800 would be just like D700: a cheaper version of the D4 which should be a nice camera: high enough MP with good noise (by today's standard, not 4-year old standard).
Although I will not buy D800 one way or another, but I do hope Nikon would keep pressure on Canon. For for now, I do not see Canon's future 5D3 would get any pressure from Nikon.