I had a D80 when I got my D7000. I got the D7000 for better low light performance and better dynamic range. I have always tried to take pictures in the dark.
When my D7000 arrived I charged up a battery and tried it without reading the manual, it's not too different from the D80 (or D90) I assume.
I do read the manual and other documentation to learn to use my camera better. I use a lot of the features. For example I have AF-S set for release priority (release the shutter even if it's not focused) because I use the AE-L/AF-L button to focus on static scenes. I've set release priority for AF-C to focus, I find I get more in focus shots of moving subject like aircraft and birds on that setting.
If you're comfortable with the D90 you'll have no problem with the D7000.
"It's not an adventure until something goes wrong." --Yvon Chouinard