I said I would break down the plot of counties in 49 states by region, but before I did that, a simpler way to break them down is simply by states that Obama won versus states that McCain won. This also didn't involve much extra work, just some cutting and pasting, and "voila!"
This shows the margin vs. college numbers in the states that Obama won, that represent a great deal of America's population, but less than half of its counties. (Quite a few of America's counties are in the south and east).
Much of this graph looks like the larger graph, especially the right side: many of the counties that Obama won biggest in are also in states that Obama won. The top of the graph looks much the same, as well. Of America's counties with over 50% college graduation rates, all of them are in states that Obama won. At the 40 to 50 percent mark, the situation is not so clear cut, although Obama still leads there. From 30 to 40, the situation becomes less muddy, but it is only at 20 to 30 that the situation becomes more muddy.
Since (as I have said many times) Obama's success was based on him managing to win both an urban/minority vote and the "educated urban/suburban" vote, the place on the left side, above 40 shows his weakest spot. Highly educated counties that voted for McCain are located in Indiana, Ohio, Colorado, New Jersey and Virginia (and possibly Wisconsin). If suburban, educated (and white) voters do deflect from Obama in 2012, those are all likely places that it could happen. Although I believe some of those places are more likely than others.
The bottom left quadrant seems to be mostly rural counties in Urban states: while Obama might have some trouble in suburban Florida, he has a bigger problem in rural Florida. However, these rural areas in urban states make up a relatively small share of the electorate.
The bottom right quadrant is also interesting: although some of the low education, high Obama counties are still there, (and are mostly black, Hispanic or Native American areas), many of them aren't. Much of Obama's low-education support comes from rural counties across the deep South, or Hispanic or Native American areas inside otherwise conservative states. So those areas don't show up on this diagram.