'Uninterested' or 'disinterested'?
Though he had chased many a flock of gulls during the course of his boyhood, by age 17 Arthur had become entirely disinterested in this activity, and had instead taken up the study of advanced chemistry.
With one notable exception, the sources I've consulted on the 'uninterested'/'disinterested' debate have all agreed that the two words properly have distinct meanings. Of the two words, these critics argue, only uninterested should be used to describe indifference, whereas disinterested should be reserved to mean 'impartial, unbiased.' Some, like Strunk and White's The Elements of Style and Bill Bryson's Bryson's Dictionary of Troublesome Words, state matter-of-factly that the two should not be confused; others, meanwhile (e.g., Follett and Burchfield) give some historical background, and then assert their preference for the preservation of the traditional distinction. Merriam-Webster 10, though, demonstrates its characteristic permissiveness, claiming that a "careful writer" may sometimes use disinterested in place of uninterested for emphasis. It then takes the issue a step further by noting that
disinterested has developed [another] sense. . .that contrasts with uninterested
--as if, just because a given usage exists, it should also be recommended (or at least condoned). Certainly, there is some grey area here, and discerning writers should preserve a bit of flexibility, perhaps occasionally substituting distinterested for uninterested based on contextual factors, including the rhythm of the sentence, and even what "sounds right." But the problem with being too flexible is that you can easily get pulled into vogue usages based on nothing more principled than the fashion of the moment or the negligent usage of the slovenly.
Therefore, I say, stick with the traditional distinction unless you have a specific, good reason to break it. And remember: if one day you find yourself in grammatical court, you should want the judge to be disinterested; if he's uninterested, though, he might fall asleep before he reads the sentence.