Apple has sold more than 50 million of its portable music players and 1 billion song downloads from its iTunes Web site. Many companies, including Amazon ( AMZN), are eager to muscle in on Apple's territory. Share of Cupertino, Calif.-based Apple have tumbled more than 20% this year, underperforming other big-tech companies including Microsoft ( MSFT) and Yahoo! ( YHOO). Analysts expect concerns about the options backdating along with possible delays in releasing the newest versions of the iPod to continue to weigh down the stock. The shares fell $2.15, or 3%, to $56.82 Friday. Intuit ( INTU), CA ( CA) and Rambus ( RMBS) are among the companies that have unveiled options-backdating problems.