The above map, via Strange Maps, overlays the 2008 election returns(Obama counties blue, McCain counties red) with 19th century data on cotton production. The resulting image is striking. We know from exit polling that the white vote in the Deep South was strongly skewed to McCain (Whites in Mississippi, Alabama, Louisiana, Georgia, South Carolina, and North Carolina gave McCain 88%, 88%, 84%, 76%, 73%, and 64% respectively) and that the black vote was even more overwhelmingly pro-Obama. Beyond that, though, what we also see quite clearly is the degree to which the African American population in the south is largely concentrated in the same areas it was over a century ago. This is something that I noticed during the primary season as well (see posts here and here).
Thus, while the Great Migration (see post here) of the early and mid 20th century saw millions of southern blacks leave the Deep South for northern cities like Chicago, Detroit, New York, Philadelphia, and elsewhere, many millions also stayed. Also, many narratives of the Great Migration note that it was not unusual for individuals or families to return to south, either because the opportunities up north were not as bountiful as they believed or because the strong ties of family, community, and familiarity beckoned them home.
On a similar note, I highlighted recent Census data on mobility a while back (see post here). One thing that you note about several of the states in this region--especially Alabama and Mississippi--is that they have seen relatively little inward and outward movement of their populations.
Over at Pollster.com, Charles Franklin does an excellent analysis of the state by state change in Obama's support among whites vis a vis Kerry's 2004 performance. He notes not only the decline in white support for the Democratic nominee in the Deep South states, but also points out the improvement Obama made in Virginia and North Carolina. Ed Kilgore over at the Democratic Strategist also comments on this dynamic.