As I have said, oh, about a thousand times before and others have before me. This IS a workable, form of birth control with high efficacy.
Planned Parenthood endorses it. Just because someone "knows someone who got pregnant while using it" means nothing. You weren't THERE, were you?
It has to be done PROPERLY. The man has to urinate before sex. If he does so, his "pre-come" will not contain sperm!!!! It's a proven, scientific fact.
This method works best with sexually experienced, mature individuals where the man as involved in NOT wanting to cause a pregnancy as the woman. The man has to have excellent ejaculation and orgasm control. It usually works best in monogamous relationships, where the people know each other's sexual ways well. I always know right before My Man is going to pull out, from his breathing and his movements etc.
It's NOT a good system for teenagers or people who have little sex experience. It has NOTHING to do with "how fertile" you are. I'm as fertile as an.. Irish-Italian Catholic.... and I have NEVER gotten pregnant from using withdrawal. However, when I WANT to get pregnant, it usually takes ONE unprotected sex event. Now, that's fertile!
Most of the time it fails because the man pulls out AFTER his orgasm has started. Teenage boys and those without a lot of sexual experience often don't know the "inevitable" feeling that occurs in the prodromal phase of orgasm. If one isn't aware of this phase, he's going to miss the window. So, I wouldn't recommend this method for people with less than, say 5 years of regular sex, for non-monogamous couples (poly couples who know each other well and have a lot of experience, of course, can use this method as well with their main partner) or for very young couples. Mainly because they are simply not experienced enough to do it RIGHT.
Done properly, it is as effective as the Birth Control Pill and actually more effective than spermicidal creme or cervical caps alone.
It's a legitimate form of birth control. It just isn't for everyone. But, them again, no form of birth control is right for everyone.