From what I got by googling a bit, Nikon D90 would be relatively a D80 notwithstanding some major and some minor pump ups i.e. boosted ISO sensitivity upto 3200 compared to that of 1600 regardless of what that H.1 and 2 in D80 would do which should stand akin to 3200 but on the D90 side H.1 and 2 would boost ISO upto 6400; Yet another modified and improved aspect would be the Advanced Dynamic Lightning which was previously available to D300 a pro DSLR but now reachable for Semi-Pros as well; and a movie mode is added which may sort of disappoint Semi-pro shooters willing to spend almost 900$ since that may deform the whole story of semi-pro DSLR into a childish compact toy/widget loaded with such eye-candies.
And the last but not verily the least, a 12 megapixel CMOS sensor which may glitter as gold in the body.