I have posted the results of some initial experimentation with the Nikon D100 at http://people.colgate.edu/rrowlett/photography/d100-test.htm. I am initially quite impressed with the image quality and ease of use of the D100. These initial tests have only scratched the surface: ISO, image mode, color mode, and noise reduction. I have yet examined variation in sharpening or tone curves, etc. or exposure metering, and have not yet tinkered with NEF image capture.
However, based on my initial tests, one couldn't go too far wrong using ISO 200-400, JPEG fine, and any of the color modes. Image processing is very good, and fine JPEGs don't lose much over TIFF. JPEG buffering and card-writing is very quick. TIFFs are painfully slow, and NEF is only slightly better.