100% Viewfinder Coverage
Nikon traditionally reserves this for its pro bodies. Nikon consumer bodies, like the D200, have approximately 95% coverage.
51-Point Autofocus System
I’ve never seen anything like it before but it looks like the AF system on Canon’s renowned 1D Series, and is probably a vast improvement over the AF system on the D200.
A New Self-Cleaning 12.3 Megapixel CMOS Sensor
The increase in megapixels over the D200 isn’t all that interesting. The self-cleaning sensor is interesting but the biggest attraction for me is that Nikon have gone from using a CCD sensor on the D200 to a CMOS sensor on the D300. I believe, or hope, that this will result in less high ISO image noise, as well as reduce the power requirements.
Cleaner images, longer battery life, better AF. Woohoo! Where’s my credit card!