Married people have better sex lives than single people. Indeed, married people are far more likely to have sex lives in the first place. Married people are about twice as likely as unmarried people to make love at least two or three times a week.

And that's not all: Married sex is more fun. Certainly, at least, for men: Forty-eight percent of husbands say sex with their partners is extremely satisfying, compared to just 37 percent of cohabiting men.

When it comes to creating a lasting sexual union, marriage implies at least a promise of permanence, which may be why cohabiting men are four times more likely to cheat, and cohabiting women eight times more likely, than husbands and wives.