Guys, I own the D800 and am a FORMER OWNER of the 5d2. What the extra MPs has meant for me:
1) Better IQ
2) Better technique required b/c of hand-holding issues
3) Better ability to crop
4) Better DR and really, better high ISO performance (vs. the 5d2)
5) Ridiculously large files
6) Average FPS but with Nikon's awesome AF it's a wash
7) Slower write times when shooting burst of images
--I love the D800, just as I loved the 5d2. IF the 5d3 had been cheaper AND fixed the banding-- it would've been choice #1 by a slim margin. I wasn't married to Canon, but getting rid of my 35/1.4L felt like a painful divorce. BTW, I will not be replacing it with the 35/1.4 af-s. I may opt for the 28/1.8 ($1,000 cheaper and painfully sharp)
I only wanted D800 for landscape shooting--which is my forte, and honestly Nikon has the UWA lens advantages for now. Canon really disappointed me with the 5d3 specs, as I felt certain that they could have done better with price and banding issues. MP count of 22 would've been alright, also.
Canon needs to improve its sensor design to accommodate increased read noise from more resolution. I know I will eventually buy into the Canon system again because, as a whole, it is more robust (and arguably better) than nikon. I'll always be a Canon fan, but Nikon made the DSLR I wanted this generation. Happy shooting to all