You couldn't pry the D800E out of my hands. I have a very early D800E. It did have the focus issue - the far left AF sensor was not accurate. But the center sensor produced some of the most spectacular, sharp images I have ever seen.
Ultimately I sent my camera for service a week before the warranty period ended. As you would expect, it was returned within 3 weeks with the problem resolved.
The issue was resolved in production months ago. It is unlikely you will experience an issue - but still possible with any camera. It's important to understand how AF works and the related issues.
First - viewing a D800 image at 100% is asking for trouble. I do it, but you are looking at something approaching 200% on the D3/D700. It is much more magnified, so of course you can see any issues.
Second - AF works a percentage of the time. Even top pros don't get sharp images every time. The tougher the situation, the more misses you have. Which sensor you use matters - cross sensors perform better than regular sensors and with slower glass, you have differences in sensor performance.
Older and lower quality lenses impact images. I have an old Tamron lens that was fine with film, but it is useless on my D800. It's just too soft. The camera can outresolve your lenses - or at least reveal any error or issue.
Your editing and sharpening techniques are camera specific. A high resolution image with a large file is handled differently. You can sharpen more aggressively. At low ISO levels you have extended dynamic range and color. At high ISO you have lower noise - especially if you are comparing images at the same output size (remember the file is bigger so it needs downsizing for comparison).
Good lenses and good technique are rewarded. The D800 produces the sharpest images of any conventional DSLR.
You asked about the 24-70. It is one of the top medium zoom lenses. Use DxOMark for a quantitative reference. It really does a nice job with D800 images.
If you are unsure of yourself, the D800 could drive you crazy. Sure there may be normal camera issues, but your issues are typically within your control and not the fault of the manufacturer. Service - if needed - takes time, but Nikon generally does a good job. Don't believe everything you hear or read on the internet - the D800 is a fantastic camera and still stuns me with the wonderful images I can produce with good technique.