For my second, I did that. I was hoping for a boy. It worked for me. I followed the suggestions in the book, How to choose the sex of your baby by Shettles. I'm lucky that I get "ovulation" pain and can tell when my egg is released. I also tracked other signs to know exactly when I was ovulating. With my daughter we had sex much earlier than ovulation. With my son, we had to really pinpoint ovulation. There are other things in the book too about frequency and more.
My friend did the same thing, but wanted girl. She got her girl. We both knew it was just a way of helping mother nature though! I would have been thrilled either way. In fact, I didn't find out what I was having, so it would be even more of a surprise.