Canon, What's Taking So Long? Please Hurry Up! by Strykapose, on Flickr
And that is exactly why I believe most people will not benefit from a 36mp sensor, they are reversing their hoods and have polarisers permanently attached to their lens, often even indoors. High MP sensors demand the best of technique to realise their potential, and, as has been pointed out, a 5D MkIII with a 24-70 f2.8 MkII actually realises more resolution than a D800 with the Nikon 24-70 f2.8 anyway, 18mp to 15mp, even on a bench test.
I would like to point out that I shoot Canon. That D800E belongs to a friend of mine that went shooting with me. The filter is not a polarizer, it is an ND filter and I highly doubt that it's permanently attached since its a 10-stop. The hood is reversed because his camera was in his bag and I needed something to test focus since I'd dropped my nifty-fifty earlier, so I used his camera.
Now to the point of mp's...when I compare my Mk3 photos to his D800E after taking identical landscape shots on the same tripod with the same (and newest...Mk2) focal length lenses, his D800E photo out-resolves my Mk3. IMHO, I dislike the D800E's colors and user interface compared to the Mk3, as I'm able to quickly setup and shoot while he's still fumbling with this buttons.
I'm not here to create an argument nor to bash anyone. I just added the caption because I was expecting Canon's higher MP camera to arrive sooner.
Like Photomoose had mentioned, I'm also basing my judgement not on speculation, but by personal comparisons of both cameras and I have to admit, I may love my Mk3 but the D800E has knocked my resolution socks off a while ago and I'm currently running around bare-feet until Canon matches or surpasses.