Well, my GP is a funny ol bugger but he's quite serious and cautious about contraception and he had this to say to me about the withdrawl method (as I was asking about whether pre-cum can make you pregnant, his swimmers don't come out until he actually finishes); "You'd have to be pretty (un)lucky to get pregnant from pre-ejaculate". I also know a couple who've been using this method and haven't fallen pregnant. Still, stranger things have happened so I'll keep my fingers crossed for you!