Opinions on pullout methods

My partner and I have recently gone on what someone could call a sex-binge. Its like our libido hit sky high and we've done it over 20 odd times in the last 3 weeks. I was already a week late for my period to start before we started and am now 4 weeks late... mind you we went the whole month before without any sex and i had my period fine. The thing is we don't often use any form of contraceptive and rely on the "pullout method". Has anyone here fallen pregnant on the method without any accidental slip-ups? Or been in a similar situation with a late period before having sex (and possibly been pregnant from it)?