I am by nature an observer and so feel comfortable observing the rise and fall of fads. Few places are as good for observe fads as a large city; I am fortunate to live in a fairly large city. My take on Apple is that its popularity could grow for a little while longer. But something is already observable, and that is that even homeless people here in New York City have Macbooks, not to mention a growing number of senior citizens and economically disadvantaged members of society.
You might ask why this is relevant? Lets go back and remember that one of the reasons for Apple's success is their advertising induced claim that it produces hip devices for "cool sophisticated" people, and that to use Apple products makes you look cool and sophisticated even if you are not, and that people as a result will look up to you. Well with growing numbers of disenfranchised people visibly embracing Apple devices, the billions of dollars marketing induced belief that Apple is a cool device is falling by the wayside very very fast. So I would say that Apple days are counted.
What will be longer lasting is the damage that Apple has unleashed on open standards in technology. So that very soon we will be likely forced into buying mediocre devices that cost a great deal more than they are worth, simply because manufactures want a bigger profitability and since Apple got away with it they will reason that so can they. We are already seeing that with some computer manufactures who think that it is more important to have a shiny device that look "good", but lacking in connectivity, and user serviceability as a consequence.