spotting trends

What is it about summertime that sends sales of colas and weight loss supplements to a high? Well, actually, the latter's sales shoot up after Christmas as well, after everyone has been gorging on food at parties and disguising the added weight under layers of clothes. Sales of seasonal products show annual trends that help manufacturers and marketers in their planning for product launches and debuts. I've always been quite fascinated by understanding and spotting these sorts of trends, something along the lines of The Undercover Economist and Freakonomics, which were both awesome books.