I've just come across another list of store closures which Borders released just yesterday. Once again, I have made a map, and it's embedded after the break. The stores on this map will be closing in late May.
It looks like 4 clusters, doesn't it? I don't think the ones in the midwest are close enough to qualify as clusters - just the 7 in the Northeast and the 7 in CA.
Out of the 228 stores, California is losing the most, with a grand total of 42 (35 before plus 7 now). After that Illinois and Florida lost the most with 17 and 16 stores closing, respectively.
View Borders Store Closures Round 2 in a larger map