In response, I took a very informal (and scientifically utterly unsound) survey of a half dozen of my fellow faculty members. My "survey" involved three men and three women, at various stages of their careers. Every one of the women I talked to had several distinct memories of being addressed inappropriately (either by first name or by "Mrs." rather than "Professor"). Not a single one of the men I asked had any such recollection, although two thought maybe they had had such an experience but couldn't remember for sure.
My colleagues offered two benign explanations for this: one suggested that students, particularly heavy users of email, are becoming increasingly informal in their social interactions overall, and that the apparent gender difference my survey revealed was instead a purely random example of that growing informality. A second noted (politely) that female professors might be more inclined to remember such incidents. Both of these explanations seem at least plausible to me, and, as mentioned, my little survey involved a whopping six people and thus obviously proves nothing at all. But if someone is contemplating empirical studies on such things, it might be worthwhile to add this to the list.
One additional note: a colleague asked me why this mattered. Maybe it doesn’t. But if the informality is gender related, and if it evidences an underlying assumption about the relative importance of the author or the work being examined, it does.