I mention this because it begs to ask: why would you want to go from a D90 to a D7000/D7100? It's a lateral move, unless you plan to shoot video. The controls aren't that different because essentially, the D7000/D7100 is just an updated version of the D90. If that's what you're going for, then great. But if you're looking to upgrade and take things to the next level, you might consider the D300s or D610. The game doesn't really change until you get into those models.
I don't really see it as a lateral, but that's just my opinion. Compared to the D300s or D90, the D7100 has.
Lower noise at higher ISO (about 1/2 a stop)
Better overall image quality (citing quite a few different tests, although only about 10%)
Tying in with the above, better color depth and dynamic range
TWICE AS MANY MP!!! Easier crop and go without losing quality. Easier to produce prints over 8x10.
5x the focus points! 15x more cross-type focus points!
Better auto-focus and processing speed in general.
Weather Sealed
4x higher max ISO
Double memory slots
Shoots faster
U1 and U2 - wow, how did I ever get along without these!!?
(didn't matter to me, but improved video options PLUS an external mic jack)
Or, perhaps this says it a bit better:
comparison
The D7100 is a nice midpoint between the D90 and the D610, and what made my decision (personally) over slaving away for another year and hoping nothing stole the funds for a D610 - All of this in a package I could afford at the moment while still making a bit of sense.
$1100 vs $1900
Granted, I came from the D3100, but a lot of people moving up the chain just don't have the pocket cash to dive into the FX cameras. If I did, I would have, but thinking on the side-business end of things, the D7100 was my starting point goal for a main camera with the eventual plans to move it to backup once I
can move into the FX world.
Obviously, different people have different motivations and goals, but that's my angle.