The D200 looks like a great body, but I think I'd wait until it was on the market for awhile to see if there are any problems. Admittedly, Nikon has better quality control than Canon, but I'd still wait a couple months anyway (like I'm doing now with the introduction of the 5D).
Actually, the D200 was the camera I was waiting for - for too long. I shot Nikon for 30 years, but when they announced the D50 - yet another consumer camera for the masses - instead of the D200 I got ticked off, sold it all, and went with Canon. Another reason was that I was constantly frustrated by the hunting focus of the 80-400 VR. Very sharp lens, but why Nikon didn't make it an AF-S is beyond me. The Canon 100-400 IS is lightning quick compared to the 80-400mm. So for MY needs (want to emphasize that) and pocket book, the Canon 20D fits me better.