A comment of mine from another blog about the importance of this in a relationship:
I agree that physical beauty fades. Proverbs 31 tells us that. Nevertheless, if you cannot be honestly attracted to your wife (or husband for the ladies), then you are doing a disservice to her by not being appreciative of the way God made them physically (because after all, we do have bodies and God made us to have that sort of attraction for a reason). Furthermore, I think that as a couple ages together and that if both the husband and wife do what they are designed to do (according to Ephesians 5:22-33), they will both grow in holiness. A couple that truly loves Jesus and does this will be more attracted to each other in every sense even if the skin is dry and wrinkly and gravity rears its ugly head.