Nikon just recently introduced the D300 and the D3, which are perfect replacements for the D200 (which I own) and the D2 (which I have never even held in my hands). The web is buzzing with discussions about replacing the “old” bodies for the new ones, and steaming with joy over the many advantages that the new stuff has over the old. The Nikon folks must be smirking in the land of the rising sun. It's just up their alley – free and viral advertizing.
 

Leave no doubt: the new cameras offer significant improvements over the “old” ones. They are improved in almost all respects. And no doubt: had I planned to invest in a Nikon body today, I would seriously consider waiting until November 2007 where these gems are supposed to hit the market.
But then again... I might just have settled with a D200. This more than excellent camera is bound to drop in price real soon now as demand falls and people do as I might have done: wait for the new models. That will open up a market for an extremely competitive camera. The D200 at 60-80% of the current price is a bargain. The D200 will satisfy even the most demanding photographer. I personally haven't nearly used mine to its full potential yet, and keep on taking still better pictures and finding new features.
 

Nikon D300 and D200 compared. Not many outside differences - but lots inside, of course. [Nikon press photos]

I see several good reasons to stay:
1) I have not nearly utilized the D200 to its extend yet. After only 15,000 shots I still feel that there is more in this body than I have managed to pry out. I keep finding new ways of getting better images out of this camera, and learn to use some of its many features: image control, bracketing, wireless flash and much more.

2) The D200 has the capacity I need in almost all respects: frame rate, image processing, autofocus, resolution.

3) The new cameras may offer better specs in many ways, and some features might seem like must-have stuff: full frame, live preview, 100% viewfinder, auto-cleaning sensor, color tracking and much more, but none of these facilities have ever been on my most wanted list, and I can easily live without. They are nice-to-have, but not needed.

I will gladly recommend the D200 any day, and I am sure that it can compete with the D300 – particularly if the price drops as expected.
 

Sure the D300 has better resolution... marginally. 12 vs. 10 megapixels is not a huge difference. It will not open a new world to you. Print in 300 dpi and you get about 1" on each side on a 10*15" print. Significant pixels to some, mayby, but not to me. They may even be better quality pixels, but I'm sure a little care taken with the D200 can produce pictures that will print just as fine as the ones from a D300.

I love the screen on the D300. The new high resolution 3" LCD is something to look at. That I would love to have, but not for the price of a D300.
The viewfinder might be better too. Haven't looked through a D300, so I cannot tell.

The High ISO performance might be better too, but from what I have read you need to jump to a D3 to really get some umph there. The D300 seems to gain a lot of its improvement from noise reduction.

No, I think my D200 has about 10-20,000 shots in it yet. I'll stick with that for now.