Dating is a thing of the past, gone the way of dinosaurs and stirrup pants. It's extinct. Kaput. Over. It's given way to two mighty opponents: In one corner, wearing matching sweats and cuddling up to DVDs every Friday night, we have the Serious Couple. In the other corner, armed with open bar tabs and clad in his-and-hers Seven jeans, the Hookup. By the looks of things, for the millions of people who bravely head out each night in search of...