I am about to buy Nikon AFS 200/2VR when my wife bought me the D300 yesterday. I have been using D200 for more than 1 year, just sold off this morning. I will share base on my experience so far and not side by side compare.
Body build:
The main & sub command wheels feel soft on D300 than on D200.
The thumb selector look cheap compare to D200.
Other than that both build to last.
AF:
Speed at start of AF D300 is faster but generally D200 and D300 no different.
Capture rate D300 is better. On D200 I have 1% AF miss and 5% need refocusing. I found D300 will gain that 5% back. Yes the continues AF is better too.
ISO:
200-400, both D200 and D300 about the same.
800, D300 has lighter shadow than D200 and better detail slightly.
1600, D300 is better while D200 suffer contrast lost at dark area. But setting D200 NR to "high" and auto enhance in software will make it the same as D300.
3200, this is why you buy D300 for. It is better than D200 at ISO1600 normal setting.
Note:
I print from 4R to A3+ from most of my shooting sometime A0 at my work place. For D200 I use ISO from 200 to 800 a lot. 1600 less often only when not doing print larger than 4R. D200 ISO 100 and 200 look the same, only when under sunny day and f-stop running pass f/16 will I use 100. I found D300 at ISO 1600 and 3200 look like matte print. They are cleaner then D200 and detail better but the contrast look funny. On base line if I print D200 at ISO800 up to A4, I will do the same for D300 at ISO3200. If you have been using Niksoftware Dfine 2.0 on D200 then I see no point going D300 unless AF is problem to you.