I'm surrounded by MD's, PhD's and PsyD's (doctors of psychology) on a daily basis. Depending on how well I know them, I either refer to them by their first name or Dr. so and so. Like my advisor and dissertation chair, she goes by first name now, but initially it was doctor. Professors I have for a class, Dr. I work for a physician for the research I do, he goes by his first name. Same for the PhD psychologist. But other doctors in the practice, they go by doctor so and so. I just don't know them well enough in my book to call them by their first name. I don't think any would be offended if I used their first name, for me it's just a matter of respect. It has nothing to do with MD, PhD, PsyD, etc. Technically they're all doctors. For whatever reason most people assume you have your MD when you go by "doctor so and so." Is that your fault if you have a different doctoral degree? In my opinion, no. When I have my doctorate (in 3 long years) I won't take offense if people call me by doctor or my first name. I won't go out of my way to address myself as "doctor" but I won't hide it or be ashamed of it either. I hear using it for restaurant reservations can get you a good table time though

By the way I have 2 masters degrees, so you can call me "master squared" around here

Or maybe that just makes me double the a-hole