The above map has been getting a lot of attention over the past day. It shows the counties where McCain actually overperformed Bush '04. We see a very clearly defined geographical region--Appalachia, especially the southern stretch--as the source of McCain's strength. During the Democratic primary, there was much discussion of Obama's "Appalachia Problem." For a refresher, the map below illustrates how deep Clinton's support was there (the more blue, the more pro-Clinton).
In a further examination of this, Ben Smith at Politico brings forward the final map below that charts American's self-identified ancestry. The same pattern jumps out as this part of the country is dominated by people who identify their ancestry as "American." In short, this is a region in which large numbers have family ties that stretch back multiple generations--very low levels of movement in and out. Thus, unlike parts of the neighboring states of Virginia and North Carolina, which have seen a much more dynamic population flow (especially Northern Virginia and Research Triangle of N.C.), this interior is perhaps more isolated from the trends and changes that have affected some of their neighbors. Virginia and North Carolina (and seemingly Colorado out west following a similar track) may have thus crossed the threshhold necessary to vote for a Democrat for the White House.