For those of us who would like a pro DX body (notice no quotes) the D300 doesn't cut it. The build is not the same. The buttons are not the same as the D2X or D3. There is not built in grip - I like the feel of my D2X. The af on the D300 is slower than the D700 and D3 due to a slower processor.In any event, I'd like to think we already have a "pro" DX body with the D300. About the only thing it doesn't have that the D3/D700 does is one or two stops of high ISO performance. But, if one can "live" with ISO/1600, it'll do just about everything the D700 does.
The only feature I like on the D300 not present on the pro bodies is the sensor shake cleaner. Some like the built in flash.