There is a shutter lag with the D1X. It's only a fraction of a second, but it's enough to cause the subject to blink or move. Maybe it's the time for the camera to turn on from standby and to fire the shutter. The F100 fires immediately. The D1X is still a great camera but the pause before firing is enough to cause you to miss a shot.
I used the camera for the first time today, taking portraits of 30 lawyers. Usually the first shot didn't count because of the delay, but the next 3-4 shots were fine. Fun to use and you can see the results immediately. The 192meg card gave me about 70 shots even though it said I only had 59 shots at the start.