from pinker's "how the mind works" - which i'm going to finish this weekend:
Confidential questionnaires asked a series of questions. How strongly are you seeking a spouse? The answers were on average identical for men and women. How strongly are you seeking a one-night stand? The women said, Not very strongly; the men said, Pretty strongly. How many sexual partners would you like to have in the next month? In the next two years? In your lifetime? Women said that in the next month eight-tenths of a sexual partner would be just about right. They wanted one in the next two years, and four or five over their lifetimes. Men wanted two sex partners within the month, eight in the next two years, and eighteen over their lifetimes. Would you consider having having sex with a desirable partner that you had known for five years? For two years? For a month? For a week? Women said "probably yes" for a man they had known for a year or more, "neutral" for one they had known for six months, and "definitely not" for someone they had known a week or less. Men said "probably yes" as long as they had known the woman for a week. How short a time would a man have to know a woman before he would definitely not have sex with her? Buss never found out: his scale did not go down past "one hour." When Buss presented these findings at a university and explained them in terms of parental investment and sexual selection, a young woman raised her hand and said, "Professor Buss, I have a simpler explanation of your data." Yes, he said, what is it? "Men are slime."
...addendum: so now that i've got evolutionary psychology in the back of my mind, i wonder how it'll affect my current and potential future relationships.