You see them in food manufacturing, many butcher shops, and most institutional food service establishments, but they haven't found their way into the restaurant world, in any major way. There may be some municipalities that require them, but I expect more and more health departments will start requiring them.
My nephew has to wear one. He has a job at a dairy plant, but I've never seen one on the job. It seems kind of funny to make a guy with shaved head wear a hat and having a cook with a beard without anything on a beard. How many guys have beards out there? How many ladies??