I have had 4 N90s, still have 1, have an F100, and an F5 too.

The biggest practical differences I have found between the N90s and the F100 are the grip and being able to focus with the AF ON button. The F100 is nicer to hold and for me focusing with my thumb rather than my index finger is really special. Beyond that the N90s has been every bit as capable a camera, IMO.