Well, I noticed issues with my focusing a while ago when taking portrait of my family members with my 50mm @ 1.8. I always make sure to focus on one of the eyes, and I've been getting a considerable percentage of images soft. I kept looking at online images from D800 seeing how sharp those are, I compared with shots from my D90 and D800 was just softer. I didn't connect the dots with the whole focusing issue at that time, so I was just purging those soft shots being unhappy with myself for not doing something right and missing opportunities.
Since then my camera was adjusted for left sensor issue, so now I don't think any of those problems apply anymore and I have to deal with problems associated with my central sensors.
I cannot tell you the exact distance that the focus misses. I never thought to try to calculate that.
With the AF fine tune parameters now, it seems that using a single sensor I manage to get sharper photographs, but then again - it's been only 2 days since I got those AF fine tune parameters calculated. So I will need to keep using them to understand how the camera behaves. The problem here is that I can use only single sensor or Live View, which is not always feasible.