The only people that want you to believe that the D300 is FAR better than a D200 are the marketing people. It has a couple of advantages, and shoots pictures SLIGHTLY cleaner at ISO 1600 than the D200 (which can be cleaned in noise reduction software so that its as good as ISO 200!).
I have my next camera going to be a D700 or D3, for me thats a proven real upgrade. A lot of people did the upgrade from D200 to D300, but its now a thousand dollar upgrade, and I am sorry if I offend anyone, the D300 is not a thousand dollars worth better than a D200.
Everytime I grab my friend's D300, its so close that you have to REALLY be pushing the envelope to see the differences... and how often does anyone shoot at those levels? Maybe 2-5% of those times?
But he also says that there is hardly any difference between D3-D300-D700-D90?! Is that really possible? Shouldnt fullframe be much bettter?
Made the Jump from D70 to D300. I have to say that there was a HUGE quality improvement. I can comfortably shoot higher ISOs with the D300. As far as between the 200-300, everyone that I have talked to who made the upgrade is glad they did.
Full frame is better, but sometimes you get vignetting even on pro lenses.
From what I understand, the firmware upgrade for the D3 helps eliminate/reduce vignetting with certain Nikkor lenses. The camera recognizes the lens is mounted and makes adjustments in the file prior to it being written to the CF card. So at least for certain glass, it is a non-issue after applying the update.