Vox reports on an interesting new study in the Journal of Experimental Social Psychology suggesting that people see "black" Americans as less competent than "African Americans". The study gave participants a fictional biography of a person variously described as "black" or "African American", and then asked them to predict qualities about the person. "African Americans" were generally given more positive attributes (higher incomes, more educational experience, etc.) than "blacks."
It's interesting to speculate on what's causing this gap. I recall reading that much of the push towards the label "African-Americans" was a belief that it would partially deracialize the group -- they were a distinct group, yes, but no more so than any other hyphenated American (Jewish-Americans, Italian-Americans, Irish-Americans). This study suggests that reasoning might have some legs to it. Alternatively, it might be that there are internal class divides within the community regarding their favored label -- wealthier or more educated persons favoring African-American, while their poorer peers preferring Black. But I have no idea if that's true.
Anyway, as the study authors emphasize, what is clear is that language matters. A rose given another name does not, in fact, always smell so sweet.