Heh - this is a good question - I'm interested to read more responses.

My (European) dad was extremely strict about calling professionals by their title. My T calls us by our first names and always refers to herself by her first name when she calls us on the phone. But we always call her "Dr.". Same situation with my last T of 8 years. I am now in touch with him socially and he's still Dr. P to me, even though the client/professional relationship is over.

The weird one is my husband's pdoc, who is in our social circle, and a few years younger than I am. Our friends would have a field day laughing at us if they heard us call him "Dr. C", but he's never corrected us on it and in fact, introduces himself as "Dr. C." when he calls us on the phone, so I guess that's the way it's going to be.