I read a book some time ago on the topic, Harlem: Between Heaven and Hell, by Monique M. Taylor, about the influx of a black middle class into impoverished Harlem showing how the issue of race, when the two parties are of the same minority, and class. The New York Times has a pretty good article from 2008 "Harlem Pas de Deux", which shows more of the class issues and hostility of lower income blacks towards higher income blacks.
The Washington Post in today's dead tree edition (it was up earlier in electronic form), covers black gentrification in Anacostia and Ward 8 in "Black Middle Class is Redefining Anacostia". I know it was up earlier because Richard Layman had typed out his thoughts 2 days ago about it.
I don't have too much to add, except to say neighborhoods change. I'm still plugging away at the 1880-1930 census project and trying to map out people on the Sanborn Fire Insurance maps. Streets, okay alleys, come and go. Places that were there one year are gone 10 years later to make way for a school, or new housing, or businesses. When I'm done with one aspect of the project I want to take it to the city directories and look at one street that went from being completely white to completely black in 10 years. I want to see where the people who left went and where did the people who replaced them came from. The only problem is that they are mostly renters, and renters are known for up and leaving after a few years. 'Tis the joy of renting.