I got tired of waiting for the D7100 a month ago with twin grandsons due the end of this month and I needed to take a landscape picture for work, so I bought a D7000 and was happy about the price. As it happened the camera had the back focus problem that the D7000 had when it came out almost two and a half years ago. Checking other forums I found three others who recently had the same experience. I returned the camera and decided to wait for the D7100.
A post I read about the D600 problems, maybe from borrowlenses.com, suggested shooting 600 pictures while the camera was in the return period and shooting a picture of a plain wall to see if the dust / oil problems appeared.
I preordered a D7100 and am excited by the specs, a great upgrade from my D90. I'll definitely be shooting a several hundred pictures the first week, but I would anyways with a new toy to play with. I'm not really concerned about getting a bad copy as I'll just return it for another.