I now use in camera sharpening whit my D200, after I notice about the same thing...It was always seem to be out of focus at 200 and 300%. After a week or two, some people on other forums was talking about if the D300 was going to sharpen more than the D200, like Canon do.
It was a problem for them. Personally, I'm not a great photoshoper and I use an old version of photoshop (6.0). The sharpen filter in photoshop 6.0 do a poor job. So unless someone give me a better version, I use and only use this in camera setting to help my pictures been selected. I know there are probably some better way to sharpen a picture, but this one seem to work.