You come back in town, and get invited to dinner with them. How do you address them? By what you used to call them (Mr. and/or Mrs.), by their first names (Fred and Jane), because you are an adult, or do you ask what they prefer?
I always ask, but I feel kind of a dork calling them formal titles when I know them so well, and first names seem like a breach of ancient protocol.
What's your take on this? Is there an official "Ms. Manners" link someone knows of? My l33t g00gl3 h4xx0r ski11z are lacking this morning.