[Mikes]

Read Mary Roach's "Bonk - the Curious coupling of Science and Sex" ... not just quite informative, but also quite hilarous. (It's not  so much about Sex itself, but rather about the history of sex research)

As a starter.... women are actually shown to be just as aroused as men by visual stimuly as proven in actual experiment (blood flow in certain areas was measured), but they are less likely to verbally state that they are aroused. (even when blood flow changes tell an entirely different story.)

I'd say that hints strongly at a cultural difference / difference in upbringing. Not a biological one.