You will find these "comparisons" all over the net. Normally it is a comparison between an apple and a banana (what has better taste).
Canon has higher Iso, so here you will find the majority of pics from Canon Fans. Nikon needs a fast shutter time for its 36MP and when the ISO is not high enough, another point for Canon.
I saw a lot of pics the last days and honestly, those from Canon do not even match those from Nikon D7000, D700, or D3 from sharpness (when done right). So I think, the Canon is a good one for Canon users who own the matching lenses and needed a better unit than the weak 5D MkII. I was curious and I was getting to buy it, but now I will wait a bit longer I think...
I saw Nikon D800 pics shot with ISO 5000, sharp like a razor knife. This impressed me really, because getting 36MP really sharp you need a top Sensor. Nikon made the real jump. Again, after the D3/D700.