I'm also just fascinated by the variety of answers you're getting.

I was going to say that I can no longer imagine caring what a person wore to an interview, but that's not quite true -- clothes so informal I wouldn't wear them out of the house, or blatantly distracting, would make me think twice about a prospie. But hair's a different matter, because it's not something you generally change every day. So I'd be looking for "appropriately groomed for the chosen style."