The tech in the D90 is probably about 3 years old now (it was released in Sept 08), so the design phase would make it about 3 years. The D7000 is new, and camera tech is advancing at a huge rate, so the D7000 just for that would be worth getting over a D90.

However any camera upgrade has to be done for the right reasons. What is it about your D90 that is restricting your ability to take great photos? This question is not about your skills as a photographer, but about the actual D90. When you can answer that question with valid reasons, then an upgrade is warranted, but if you want to upgrade cause you 'want a better camera to take better photos', then you need to look at YOU, not the camera, The D90 is quite capable of producing stunning results.

Two ambiguous paragraphs? Yep, but that was on purpose to make you think about your reasons for wanting to upgrade!