I wore my tux on formal night and my suit on semi-formal. That being said, and perhaps it was because we had the early seating, I only saw one other gentleman wearing a tux. There did seem to be more tuxes waiting to enter Lumiere's for the late seating.
That being said, I would estimate that on formal night, only about 2/3 of the men were wearing some sort of coat and tie, with that number being much lower on semi-formal night.