How effective is pulling out?

[Diggslick]

So heres the deal,

Hooked with this girl about 2-3 months ago. Knew her through friends. First time we hooked up(catastrphicallly drunk) we did it without a condom. Since then, we've been hooking up a couple times a week. Its been hard to get in to the habit of using one. The girl said that when she had tried the "standard" pill a couple of years ago, it really messed with her body, but was looking in to some other types of birth control. She seems to keep procrastinating on this.

I know for a fact that the girl has been with very few people, so I'm not worried about catching anything. I Am worried about getting her pregnant. I pull out everytime. I never really have had a problem about knowing when I'm going to come. I wondering how effective this is and how likely there is to be an accident. I went to catholic school,(not a pantheon of birth control info) and they used to tell us all these stories about your body releasing a little sperm early to clean things out before you ejaculate and that you don't really know it.

I'm looking for some practical info.