Female sperm have a larger head, they swim slower and do live longer. Supposedly BD'ing two days before ovulation rather than day of can help produce a girl but I don't like taking that risk. I bd'd two days before ov, the day before and day of and have a daughter.
I'll be curious to read what others say. We are hoping for a boy this time but will still be very happy with another girl (and won't have to worry about buying any new clothes!).