I also moved from a D90 to a D7000. I was completely happy with the D90 but I upgraded for the increased flexibility the D7000 offers and for the dual memory card slots - not because I thought it would give me better photos.
A defective SD card in the D90 cost me a day's shooting and it really got under my skin, so having the in-camera backup became the tie-breaker for me. Then again, maybe I just wanted a new toy and that was the excuse. It's hard to tell sometimes.
As Tom said, you might want to consider spending the $1200 on glass rather than on a new body unless you need or want a specific D7000 feature. The D90 is an excellent camera. $1200 comes close to getting you a used 70-200mm f/2.8 or a brand new Tokina 11-16 f/2.8 paired with a fast prime. The D7000 does work extremely well at high ISO settings, but fast glass wins over high ISO.