You can call me doctor, and I will not be offended. But I prefer professor. Hey, dude! or Steve! are clearly out of abounds for a first time approach from a student.
This piece actually surveys academics and finds that US/UK cultures are a bit different. As I said, I prefer professor since there are all kinds of doctors in the world but professors are a distinct brand of folks. I can see why some folks might want to be called doctor, since they have earned a doctorate and all. Either one is going to be fine most of the time. Informality is fine after a relationship has been established and expectations have been set.
And, yes, of course, women probably get more grief and are treated more informally than the men. Miss, Mrs., Ms. are all << to prof/doctor.
Yes, I have blogged about this before, but now folks have data! Woot! Anyhow, the problem, of course, is that the most likely offenders are the least likely to be aware ... well, of anything, but certainly of blogs that provide some stats.