From a recent collection of studies (unfortunately the link is not longer active) aimed primarily at women (excepting the last), it seems that frequent sex can… (to be said very quickly in one breath):
Decrease stress, relieve pain, relieve depression, develop your brain, decrease incidence of brain cancer, assist in your sleep, help you loose weight, help your immune system, decrease hot flashes, keep your organs healthy and elastic, noticeably assist in appearing younger, and reduce risk of prostate cancer and heart disease by nearly 50%. (Breath)
And, in case you forgot. It is fun. In these economic times, it also seems to have the ability to save quite a bit at the pharmacy.
Considering the previous, this report, how birth control pills may improve your memory may have more to do with a possible accompanying increase in sex than the actual pill. But that is just my opinion.