More than two million couples wed every year in the United States, bringing together a whole new family unit. The extended family may now include a hard to please mother-in-law who criticizes her daughter-in-law's childrearing; or a patriarchal father-in-law who expects all the kin round the dinner table every Sunday; or a new spouse, who a year or decade out, still gets shellshock visiting the in-laws. If that wasn't cause enough for a stiff drink,...