I have just got the D7000 as an upgrade from the D200 (not a D300 by a long way I know) but the improvements are vast. The noise levels at iso 1600 are hardly noticeable on a correctly exposed shot and are only evident at higher magnifications or crops at around iso 3200.
The big jump in pixel count is pretty impressive too. I have not had a proper chance to use in anger on a landscape shoot as yet but will be out this weekend hopefully.
Build quality is reasonably substantial as well, although not as heavy or solid as the D200 was, it is still partially magnesium alloy framed and has the dust and moisture seals of the D200/300 cameras.
The new metering and focus works like a dream on subject tracking in the 3D mode. I could never quite get it work on the D200 so didnt ever bother using it. Would be a boon for wildlife togs with a fast lens attached.
I would highly recommend the D7000 to anyone considering an upgrade or new camera. I got the 18-105 VR lens as part of the kit which is fine as a general purpose carry around, but will be switching to the Sigma 10-20 as soon as I hit the hills
Regards
Richard