I didn't go see the 171-minute Avatar this weekend, but I know many people who did and when confronted about the big Jake-Neytiri sex scene, it wasn't a big talking point. ("Oh yeah, I don't know, not much, etc.")
And then I saw a quote from James Cameron this morning where he attempted to downplay the additional scenes beforehand: "Just so that we correctly manage people's expectations," he explained carefully, "it does not change our rating at all. I would call it more of an alien foreplay scene. It's not like they're ripping their clothes off and going at it."