I was once faced with a situation where I felt my novel needed sex scenes (Peaceful Quiet Lives). In an attempt to avoid ending up with Bad Sex Writing ridicule (an ignominy that even afflicted Sebastian Faulks with the otherwise astonishingly powerful Birdsong, one of my favourite novels) I consulted a few romance/erotica novelists I know, and was advised to "sell the sizzle, not the sausage". I think I understood what that meant, so tried to apply it. :)