I went off the Pill in Sept of 07 and found out on Feb 14 I was Pregnant. I used the pillow under my butt each time my DH and I had sex. It apparently worked since I was preggo in Feb. I am a picky eater and didnt have very good eating habits, so we think that could be the reason I lost the baby the last week of Feb. Then we werent exactly trying again but we werent doing anything to stop me from getting pregnant, so I found out April 10 that I was pregnant again, but I lost that one the last week in April as well.
I've tried the butt under the pillow and the hips raised in the air, my DH even held my hips up high for me one time.

It is possible to get pregnant this way, but like the others said, you need to know when you are ovulating. That is the best way to find out what days you are fertile enough to try and hopefully get pregnant.
Good Luck!!