Image quality: I find it a bit too noisey for the money, and somewhat lacking in detail. Not a big enough imporovement over the 5MP Sony F717 to justify the cost difference. In some instances the Sony is better.
Overall quality: The F717 seems heavier duty, it is all metal and although the body is smaller, it feels heavier that the D100. Not a lot, but a nice solid piece of work compared to the plasticy Nikon. The D100 feels hollow, cheap for an expensive DSLR. The menu systems are not very intuitive, and sometimes the camera won't take a picture until you get out of them.
The D100 looks and feels just like my old N60 only lighter. It acts and sounds just like a 35mm SLR, the camera internals are the same except with a sensor in place of the film strip. In fact a co-worker, and long time digital user, was checking it out and couldn't figure out why it was "all blurry" when he looked through the view finder. He also had a hard time finding the "zoom button".
I highly recommend this camera. If you were reluctant to switch to digital because you loved your old SLR then this is definetly the replacement for you.