I've recently gotten into an online argument (it's like the Special Olympics, I know), and in the course of this argument, I realized I was switching back and forth between first and last names.
For the last ten years, I have either been a graduate student or an enlisted soldier (or both). Which basically means that when I wasn't calling someone "sir" I was calling them "Captain something" or "Professor something."
I think one of the biggest, but subtlest changes, after finishing my dissertation (and almost finishing my contract), has been moving to using first names for professors and officers. Its an odd shift, calling someone "Mike" or "Bill" instead of Professor Smith or Captain Green. (Especially when the name is "Bob" which is my father's name, and constantly freaks me out). Assuming I ever actually get an academic job, referring to other professors by first name I'm sure will be as big of a shift.
But this whole thing has gotten me thinking about first and last names. On the one hand, as a friend of mine put it "he asked me to call him Bob. I don't know, it's like 'no, I respect you too much to not call you Colonel." What's interesting is at the same time, I have used first names to denote respect, and last names as a subtle insult.
I think this is very similar to the technique a sergeant has for making a "sir" into an insult.