Gregory's article pointed me toward several new authors and texts I need to check out, so it has turned out to be very useful. But more so than that, i see Gregory's contribution to my work as such: he complicates the concept of "black metropolises" to include a more optimistic, dynamic view of urban space. Whereas Richard Wright, just to give you an example, portrays Chicago as a dismal, hopeless place, Gregory invites us to see how these black metropolises were the location of change and growth for black communities (in the North as well as the South). He also connects northern and southern cities by showing how the social and cultural changes in the North affected (and in turn were affected by) southern cities.
All in all, Gregory gets an A in my book. I need to read his intro and Chapter 1 to learn more about his use of the term "diaspora," especially since he's the first person I've heard refer to black migration to northern cities as "diaspora" (this term is often used to describe the migration of Puerto Ricans to the U.S., which leads me to think there's something going on here.)