i ride a women's frame. see, it was custom made for me. and i'm a woman.
i also used to have a woman-specific road bike.
both are full triangle frames. they just have a shorter top tube. they fit.
btw- rivendell makes one of the most awesome, drop-dead gorgeous step-through frames on earth. ch-ch-check it out:
i saw one on the streets of chicago, and man... wow.