Well, let's run the numbers. I'm thinking, mathematically, that "99% effective" means, if a woman using the contraceptive has sex once a week (something the "Sex in the City generation" would consider pitiful), that within two years of starting the contraceptive, the law of averages will catch up on her, the contraceptive will fail, and she'll become pregnant. Of course, this'll happen sooner if she's more sexually active. Then what happens?
Am I missing something here? Then again, I'm also the guy who figures that milk that is 2% lowfat still has 98% to account for.