I recently read an article about a study regarding caffeine as a sexual stimulant:

"[Researchers] gave 108 female rats a moderate dose of caffeine before a mating test to determine if the caffeine had any effect on female mating behavior. They found that administration of caffeine shortened the amount of time it took the females to return to the males after receiving an ejaculation, suggesting that the females were more motivated to be with the male rats."

The article went on to speculate that caffeine exposure could also affect sexual motivation in other female mammals, such as humans.

You know what's sad? There are 108 female rats that are getting more action than I am... Hey, if they ever want to test this theory out on humans, I'm sooo there.