I agree with Wombat. Are we more liberated than we were in the 50's? Certainly, though probably not much more liberated than we were before the Hays Code went into effect (it's easy to think of pre-1960's women as being buttoned up and proper and Victorian, but you have to remember that after WWI and the success of the Suffrage Movement women became much more open about their sexuality, especially in the roaring 20's. They might have been conservative 70 years ago, but not 80 years ago). But the public dialogue in America regarding sexuality still comes from a place of shame and apprehension. I'd argue that the extreme lewdness you see in some facets of pop culture is actually symptomatic of repression, rather than evidence of its absence.
Is it acceptable to talk about amongst friends? Yes, but it always has been, more or less. The measure of our societal attitudes toward sex has to exist in the public domain rather than the private one. We can talk about sex in public but it's usually frowned upon, if informally. More importantly, public nudity, and public displays of affection or desire, are still strongly reviled. I remember being 15 and being totally floored when I went to Paris and the newspaper kiosks were selling lad mags with bare tits on the cover. Right there out in the open, stapled to the outside walls of the kiosk, shapely, naked breasts. You would not get away with that in America. It's considered risque to just put words of a sexual nature on the cover of a magazine here.