People I know have used this method and have never got pregnant. (withdrawal)
As for ovulating, my friend got pregnant 1 week or less after her period, as she obviously ovulated very early, she knew it was then as they BD, and then her husband went on a business trip for over a week, and by then he was back she was already full of symptoms.
There is no fail proof method for not getting pregnant, except abstaining. You can fall pregnant on the pill, even. Not likely, but it happens.
That said, I think withdrawal works just fine if you are not 100% against a pregnancy. The only way it fails is A) failure to pull out obviously or the man not knowing when he is going, or B) Pre-cum containing sperm. But pre-cum
does not come from the same place sperm does. It is advised that the man urinate after any prior ejaculation to flush out sperm, sperm cannot withstand the environment after that. So IMO, thats a pretty good guarantee if you consider the dynamics of how it all really works and are careful to do the things needed for further protection. Plus, studies have shown the occasional detected amount of sperm IN pre-cum, to be extremely
low, to the point of being considered "infertile", because they are almost completely immobile and are extremely low in numbers to qualify as fertile.