Not too much comment, because my neck kind of hurts right now, having been staring at a glowing box all day, but:
With a few minor exceptions, the counties all line up pretty directly, meaning that there is no major breach or rearrangement between 2008 and now. Not to say that the 30 point shift between Obama's margin and Coakley's margin isn't significant, but Brown didn't get there by targeting some special region or demographic.
When I was looking at the graph before, I thought Middlesex would be the cut-off point, just because of its name. It seems Middlesex was not EXACTLY in the middle (although if it would have followed the 30 point drop exactly, it would have been), but it was pretty close. I didn't really know how Massachusetts population broke down, but apparently the most liberal counties are not actually that populous.