I agree with antmanb. I'm happy to call people whatever they prefer; I just hate the awkwardness of not knowing. A lot of students call me Mrs hoptoad, but it doesn't bother me enough to correct them. Let's just adopt "san" for everyone.
I get annoyed every time I see a box for Mrs/Ms/Miss on forms. Men don't have to declare their marital status OR their preference to not be identified by their marital status. I usually leave it blank, as my name is just fine without a title. Even though I hate that box, I do wish there was a title indication for parents in our school's database, so I'd know what they prefer.