Since I know this thread was in part started due to my conversation earlier and because of a question posed to me, I should probably give some reply. I have been moving, so I have been extremely busy, and even without Internet for a couple of days.
Briefly, seldom does sex advance the story. And I don't care how arrogant it sounds, I don't believe in sex before marriage, and I wish movies didn't show it as not only acceptable but even preferable: apparently only losers wait. This really is a common theme.
Even if sex is part of the story, or acceptable, how much do we have to see to know what is happening? Alfred Hitchcock implied sex scenes without even showing anything more than passionate kissing. Today we have to see a lot of skin for lengthy amounts of time. It doesn't matter if it arouses. It doesn't matter if actually shows the nipples or the butt cracks or whatever. It's trashy and unnecessary. We all know what sex is, but movies these days try to make it more and more risque in order to, as was said earlier, though with different intent, appeal to the lowest common denominator. Why not show a little respect for the human body and for sexual intimacy?