It depends how tall the woman is it seems - all of the discussions I have had recently with LBSs centred around if the woman is 5'5 or below, then there is some value in a ladies-specific frame, over 5'5 the difference in body shape, length etc is less different between men and women, although women generally do have proportionally longer legs.
The one thing that is definitely a must is a ladies' saddle but that's an easy £30 swap
I am 5'10, not exactly skinny and needed a shorter stem and narrower bars on my new road bike (54.5cm frame). I also ride an XL Sirrus, feels big, have also swapped to a shorter stem. Both bikes have women's saddles, men's ones are uncomfortable