My first DSLR was the 20D back in 2004. I bought a Nikon D700 the summer of 2008 and sold all my canon gear. I switched back to Canon because of more resolution and video ability mid 2010 in the 5DII.
My first reaction when the specs for 5DIII and D800 were clear, I have to admit, I was disappointed. I wanted to switch to Nikon again, the ratings from DXO Mark on D800 were also very impressive!
After some time to thinking, for me it all comes down to the lenses. Most of my work is in portrait and I use my 70-200mm II IS very much. For me, it is clear Nikon has a edge in wide angle lenses, but in longer optics I feel Canon has the edge.
The way I see it, both cameras have strengths and weaknesses. I have been shooting more and more video this year, and the issue with green cast on the screen of D800 is a issue for me in regards to video.
The biggest print I have made is 1.5 x 1.0 meter and I was very happy with the results (from my 5DII). I would prefer that Canon went with more MP, but what they did is also fine by me. I do a little bit of reportage and the extra ISO and speed might come in handy.
If I still had my D700, I would go for the D800 and get my self a external monitor for video. The D800E is also very attractive, having D800 and D800E would be a dream.