You know women who aren't gentle & sensitive & curvy, and you still consider them feminine. But (per Wikipedia <http://en.wikipedia.org/wiki/Femininity>) our culture sees those women as less feminine, the more aggressive, angular, and non-heteronormative they are.
My issue with the word is that it tends to make it easy to forget the distinction we're talking about. When I say a woman is butch or aggressive or non-nurturing, people hear "less feminine." That should be "less stereotypically feminine," but I think it's inevitable that when people hear an unqualified "feminine" they understand it to mean "stereotypically feminine."
So all I'm saying is that rather than having to say every time: "by feminine, I mean like-a-woman, not stereotypically feminine," I encourage people to think about what they actually are trying to convey with the word feminine, and say that instead. Usually, they don't just mean "like-a-woman." Usually they have a particular, stereotypical trait in mind.