I was brought up in two worlds, the egalitarian American one, and the much more formal European one. As I said, in academia - even in the U.S. - I would use the formal "Dr" or "Professor" in cases of doubt, although I have long been on a first-name basis with most of the persons that I work with. (Except my secretary. For some reason, she prefers to be addressed as Ms [Surname], and I have always respected her request.) As for my students, I expect them to address me as “Professor”.
When I worked for the government, in international affairs, the default option was the title, or the title plus the surname. There are just so many different cultures, and the uninvited use of the first name can sound condescending. So, yes, it was almost invariably "Madame Ambassador" and the like. Once we walked out of the meeting room and to the cafeteria for lunch, we would now and then use first names, but as soon as we returned to the formal negotiations, I would generally slip back to using the honorific.
That, however, was at work. As many previous posters have indicated, the situation is different if the only contact you have with someone with a formal title (Ambassador or whatever) is in a private setting, for example as your neighbor. I would introduce myself to a new neighbor as [first name] [last name], and then see how he or she reacts, and take it from there. I am old school enough to expect that children address me as Mr [last name], but am quite flexible as to whether other adults want to call me by my first name or as Mr [last name].
And while we’re at it – and not that it would ever happen – if I should bump into a former President, I would definitely refer to him as Mr President.
You're right. In my case, I started with the J.D. degree (which, in the U.S., is the basic law degree) but then continued to get two more degrees in Europe, with the second one being the J.S.D. degree.
