Had the D100, now have the D200 - of course with the saem lenses. The image looks a little cleaner, but not Earth-shattering.

Yes, the resolution doesn't go the way numbers might imply on the surface - the D100 (6MP) had a native res of 2000x3008, and the D200 (10MP) has a native res of 2592x3872. Just over an inch and a half larger for a 300dpi print ad - nothing to write home about.

BUT, the D200 images up-res with the Nikon capture software to 3000x4500 MUCH better than the D100 (which came out looking softer). This is mostly where these numbers in sensor MPs shine - up-resing from camera RAW images.
-Lew ;-)