When should investors sell their Apple stock?

Reuters reports:

When should investors sell Apple shares? The group’s push overseas and into the business market still holds promise, as does the steady stream of fresh gadgets such as Apple TV, unveiled by chief executive Steve Jobs last week. Apple’s trajectory should continue for some time, so its stock — which has gained more than 40 percent each year for the past five — looks attractive at 15 times estimated 2011 earnings.