I made the switch from D90 to D7000 about a month ago, and I had the back-focus issue. The D7000 has a feature in the menus where one can fine-tune the autofocus if the camera back- or front-focuses. In my case the back-focus was worse than what could have been corrected through the a/f fine-tuning feature. I dropped the camera off at a Nikon repair facility and they made some adjustments. I have since then been able to fine-tune the a/f to the point where I believe it's just about as good as it can be.
The D90 is a great camera and I was very happy with it. The D7000 is just that much more capable in most respects, and a very worthy step up from the D90. If you were happy with your D90 you will probably love the D7000 just as much, or even more. As for back-focus, if your camera has it, it's easy enough to fix, either through a visit to a Nikon facility, or adjusting the a/f fine-tuning yourself, or a combination of the two. Remember, it's not just this model that has the occasional a/f issue.