I just did a bunch of testing with mine using a 17-35/2.8 at 35, focus distance about 2.5 meters, and the left hand focus point yielded distinctly blurrier results. However, I was a little suspicious about this, because the blurring appeared to be primarily horizontal, which would be either symptomatic of camera movement (unlikely given that I was using flash at 1/250) or astigmatism, which is a lens characteristic.
Repeated the test with a 35mm f/2 prime and all the images were sharp, with the left focus point being sharpest by just a hair.
I have definitely seen test images from others that show serious problems with their left focus point that are way beyond anything I saw, so I believe it's a real issue for some cameras. However, I also suspect that people who test and return six or seven cameras probably should do their best to make sure they're not seeing aberrations originating from their lenses.
Pro zooms have gotten good enough these days that people assume that they perform as well as primes, and in many circumstances the differences may not be important, but if any camera's going to show up the difference, it's the D800.
This may be the case (many poorly done tests) but in my case, I tested on a tripod, mirror up, with a 20mm f/2.8 a 50mm f/1.8 and a Tokina 28-70mm f/2.8 at 35mm. With indoor lighting and an EV of about 4 or 5, I was able to achieve razor sharp results with the center and right sensors with all three lenses using NO AF fine tune. The exposure settings for the 50mm hovered around 1/60 f/1.8 ISO 400.
The left was only sharp 1 out of 10 tries. I can't really explain the 1 sharp example from the left sensor, but each time I tested I racked focus to infinity so my guess is it just got lucky. That said, even when the left AF sensor was sharp, it was only "acceptably" sharp. It still did not compare to the center and right sensors by a long shot. Additionally, when focused with the center sensor, or LV, that same area on the left of the frame was rock solid sharp. I find it difficult to believe that in all of my trying I could achieve pin sharp results using center, right, and LV but nearly never with the left.
I also did some tests with flash using an ISO of 100 and shutter of 1/250 (aperture f/1.8) putting the ambient light 4-5 stops below proper exposure (to reduce the affect of camera shake, if any). My results were the same. The left AF sensor never produced sharp results.