Wherever I've worked, we always call doctors 'Dr So and So'. I've never been anywhere where they are called by their first name. They call nurses by first name.
I'm old-fashioned in this way. I feel that MDs deserve this respect. I'm in no way groveling and generally enjoy all the doctors I work with, especially the more seasoned, experienced ones. Some of the younger ones have yet to develop into interesting people, and tend to lack great social skills.
I also address my children's school teachers by Mrs or Mr and their surname, even if they try to get on first name basis. I come from a different generation where people were more formal. When I was a girl one did not address any adults but your parents' close friends by their first names.
Is this changing in some places and how do you feel about this subject?