I saw in some sex documentary once that basically, a woman's lips (face) are a direct representation of her lips (labia), and even provide more visual stimulation by becoming red and engorged when she's aroused (think sexy parted lips, red lipstick, lip liner, etc). Plus what fordie said about fluff-suckin lips - the bigger they are, the better she'll do!
With that said....I'd bang that like a bongo drum! :-)