Shares of Amazon.com (NASDAQ:AMZN) were up more than 40% last week after the online retailer reported better-than-expected earnings. What's behind Amazon's rebound? Should investors buy it? Will a downloadable music service click with consumers and allow Amazon to compete with Apple (NASDAQ:AAPL)? The Motley Fool's Mac Greer talks all things Amazon with senior analyst Rick Munarriz.