i think it is super sexy when women do it. based on what i know, vaginal intercourse by itself is not enough for most women to orgasm. might as well help yourself to an orgasm while the man works himself to one too.
not sure why we don't see this in porn more. oh yeah, porn is made for men. and we are supposed to believe that a man's penis is enough to cause a woman to orgasm. me, i'd rather see a woman have a real orgasm.