So I finally came to some resolution over the focusing issues I was having. I won't bore y'all with too many details, but the end result was basically that I swapped the 17-55 DX for a 28-70. At the end of the day, this lens was the problem that was biting me in actual use shots. I was able to convince myself the camera was a problem beyond that. I would say the only thing Nikon could have done better would have been to let me know what was up as it went along. The last replacement they sent me had been tweaked to utter perfection before they sent it to me. This explains why it arrived with ~60 shots already taken. Had I known that I would have ended up leaning on that lens a lot sooner. They were extraordinarily kind and helpful to me, and have earned my loyalty three times over. In conclusion I would say that different lenses simply behave differently when it comes to focus. We were able to readily prove, for example, that the 17-55 and 28-70 place the DOF in different spots at the same focal length, focus and aperture, regardless of the camera. The effect was more subtle on my other Nikons so it never attracted my attention. I do not know if this a matter of optical design or electronics. I tend to think it may be the former. I am a new fan of the 28-70. I don't agree that it is less sharp wide open. If anything I would say this one is more sharp than the 17-55 I had.