Megan McArdle

Department of Awful(ish) statistics:

"The best explanation may be AIDS; unprotected sex is riskier, so people are having much less of it. The fall roughly matches up with the widespread change towards perceiving AIDS as a heterosexual problem. But that's an offhand guess. We really don't know why the abortion rate has fallen, though I'm sure we're all glad it has."

Yes we are, though I'm willing to bet there are some out there who think this is a bad thing. Interesting reading.