I've had both, I recently sold my trouble free D90 and I just had to send my D7000 in for service. The D7000 has a more robust body, better body controls, and better features. The IQ between the two is basically a wash. Take the same picture with both cameras and it is very difficult to tell the images apart. The only reason to pick a D7000 over a D90 is if the D7000 offers features you need that are unavailable on the D90.
I probably should have listened to my initial instincts and passed on the D90 to D7000 upgrade.