After reading many of the posts here, I get the feeling that most of you didn't actually sit down and read through the 25 sections of dpreview.com's very detailed analysis. It seemed very objective, and after reading nearly every word (as opposed to skipping to the conclusion), I came away with a different take: the reviewers like both the 5DIII and the D800 a lot. They haven't posted their formal review of the 5DIII, but it's obvious that it's going to be well received. I bet it will be within a couple points of the D800 when all is said and done.
You all should take a look at this one particular section of their review (particularly Overall Image Quality, paragraphs 2 and 3):http://www.dpreview.com/reviews/nikon-d800-d800e/23
They specifically point out a few things about the resolution:
1. To get the most out of the sensor, you need impecable technique, an excellent tripod, a cable release, shoot with mirror lockup, and generally plan on higher shutter speeds. Honestly, I'm not good enough at photography (nor do I want to use a tripod or high shutter speeds all the time) to attain medium format results. I bet most of the strident posters on this forum are equally mediocre with their technique as I am. Sure, the D800 does well without perfect equipment and form, but not at the incredible resolutions people seem to think they will get. That means you often have 70MB files that aren't really getting you the sharpness you pretend will magically appear.
2. High end glass matters significantly with the D800. I don't have the cash to have all my lenses be multi-thousands of dollars each.
It's the Internet, folks. Anyone can say anything, but I think dpreview's reviews are pretty credible (more thorough and unbiased than any other site I have found). I think if you actually read through the whole thing and analyze the comparison images on resolution, noise, high ISO, etc., you will come away thinking, "Huh. Both of those cameras are pretty darn good, and not really that different."