Page 447 of the text states that people prefer faces that are more "averaged" and symmetrical. This goes for more than just how we see people. According to a study of 86 heterosexual, sexually active couples, women have less orgasms is their partner's face is asymmetrical.
So as odd (and maybe slightly awkward) as it may be, women are more likely to have an orgasm with a male partner who has a symmetrical face.
There may be Biological and Evolutionary explanations to this phenomenon.
As I learned in one of my Biology courses, the female orgasm assists with transportation of sperm (via muscular contractions inside of the vagina) so that they have better access to the egg they need to fertilize.
As mentioned in the book, we sometimes see asymmetry and other facial imperfections as clues that our partner's genes are inferior.
We want to mate with people who have good genes so that our offspring will have a better chance of survival. So if women are with a mate who they think posses those genes because of their facial symmetry, then the women are more likely to orgasm and get those sperm over to the egg.
Source: http://www.sciencedirect.com/science/article/pii/000334729580014X
