While I was shooting with my D80 I was drooling over the D90, but when the D7000 was announced it wasn't a tough choice. I've had the D7000 since early November and love it, but discovered a reality.
The D7000 is more demanding than my D80 (and your D90). I need both good glass and excellent shooting technique to get the absolute best results. My new best friends are the D7000, 50mm f/1.8 in low light, 18-55mm VR in daylight. I do a lot of hand-held with great results and use a tripod for ultimate sharpness.
The 18-55mm will be upgraded in the future, but in good light that lens provides pretty decent results.
Good glass and good photo technique will, I believe, provide the delta between the D90 and the D7000 you're looking for.
"Red is gray and yellow white, but we decide which is right ....and which is an illusion"