I've got a step through ladies frame, it's brilliant.
Yes, I ride in skirts/dresses, so its good from that POV. BUT I also have a little problem with balance (left over from having a slipped disc). Cocking my leg over the the bike didn't work very well for me (Most of my falls have been when getting on or off the bike!), the step through frame is much better for me from a balance POV.
I've also seen that men quite often prefer them if they've got a toddler seat on the back as the baby is in the place where you usually swing your leg over.