If you haven't yet finished buying Christmas gifts for your nieces and nephews and the neighbor across the street, maybe you shouldn't bother. That's right, don't buy them gifts this year -- or ever; it's an economic waste, says University of Minnesota economics professor Joel Waldfogel. Twenty years ago, Waldfogel coined the "deadweight loss of Christmas" theory in a small paper in the American Economic Review. His research, popular with the media this time of year, has gone on to have a life of its own. And Waldfogel followed it up with the 2009 book "