First off is the sex scene an important part of the book? If the book is primarily about sex the chances are I am not reading it as that would just bore me to tears. The sex in the story isn't always the most appealing or even exciting part but it has a part to play none the less in my opinion.
Take for example the book I am reading now, "American Pyscho". Very graphically described sexual acts in a gutteral way that are extremely unpleasant but they give a valuable insight into the mind of the character, so their place in the book is warranted.
I may be well off here but I'm yet to see a film or read a book that details a sexual encounter that has had any real affect on me or my enjoyment of a story. Sometimes I'm glad the characters got together or other times I'm just being a perve but in no sense is it down to the script or the narative of the scene in question, it is always about what was before or after.