I try to get inside a woman's head when I'm writing her, but I don't know how well I succeed -- men are terrible at getting inside women's heads. I've heard that romance readers can tell within a page whether the writer is male or female, without knowing the author's name.

You've hit on an interesting point of discussion. How many of the differences between men and women are physiological, and how many are cultural? There are certainly some areas in which you could argue *most* men differ from most women.