I've walked out of my dentist's office before. Told his receptionist that I had better things to do than wait around for him and that I would call to reschedule sometime. Obviously it was a routine app't, not an emergency. He was over an hour late and my time is just as valuable as his, especially since I was missing work to be there.

He called me personally that night at home; apologized profusely and booked me in as his first app't the next morning. Usually takes up to four months to get a non-emergency app't with him.

I don't know if he made some kind of note on my file, but he's never been more than a few minutes late for an appointment with me since!

I think you were perfectly justified!