The new study shows that by age 20, 75% of Americans have had premarital sex. That number rises to 95% by age 44."
Source: http://www.webmd.com/sex-relationships/news/20061220/premari...
It's just that the doctrine isn't working, and it never has. Teaching people about condoms doesn't increase non-monogamous sex ratio's (those are high already), but it does increase condom usage. The guilt and exceptionally "sex-negative" culture that's been fostered in Western Culture, a large part due to Christianity, has caused us tremendous problems through sheer ignorance of human sexuality.
Unfortunately, it's often the women who are at the most at risk, even those in monogamous relationships (women are at a much higher risk of AIDS infection) as it's statistically the male who cheats and in many societies the ability to divorce is limited. This doesn't even touch on the power birth control and condom usage has given women in fully monogamous relationships to properly and effectively plan their pregnancies.
Oh, and should this even be hackernews?