I just wanted to add my 2 cents: I don't think it hurts, but it can help them to remember you if the committee meeting is a long time from the interview. When I was accepted at one of my schools, one of my interviewers called me to tell me. He even said "Thank you for the nice little note you sent." All I had said was that I had a great time there meeting everyone and that afterwards I drove around town and he was right, Lexington was a great place to live. (He had talked about how he'd lived there most of his life, etc).