While shareholders have been spooked by founder Steve Jobs’ illness, there’s a greater threat out there to the company’s long-term prosperity. Apple’s success in recent years has been with innovative but premium-priced products–iPods, iPhones and Macbooks. But the “netbook,” a smaller and cheaper version of competing Windows-powered notebook computers, is cutting into Apple’s revenues. Macbooks have been responsible for much of Apple’s profits in recent quarters, but as the economy has turned worse, netbook sales have beaten Apple market share down from 9.5 per cent to 8. One netbook winner: Taiwan’s Acer, which displaced Apple as the fourth-largest purveyor of portable computers in the U.S.