Amazon Prime may be the most ingenious and effective customer loyalty program in all of e-commerce, if not retail in general. It converts casual shoppers like Tinsley, who gorge on the gratification of having purchases reliably appear two days after they order, into Amazon addicts. Analysts describe Prime as one of the main factors driving Amazon’s stock price—up 296 percent in the last two years—and the main reason Amazon’s sales grew 30 percent during the recession while other retailers flailed. At the same time, Prime has proven exceedingly difficult for rivals to copy: It allows Amazon to exploit its wide selection, low prices, network of third-party merchants, and finely tuned distribution system, while also keying off that faintly irrational human need to maximize the benefits of a club you have already paid to join. Read the fully story on Businessweek.com.