Dietrich Kappe has done another of those social network studies of book consumption using Amazon’s
Other Customer’s also Bought...
(The original (at least, the first one I heard about) being Valdis Krebb’s Study of polarised political book buying).
The graph isn’t so pretty as Krebb’s, but it is more interesting in that it shows a more complex picture than the rather-to-be-expected left/right political divide of American politics.
If you’ve written or read similar studies, I’d appreciate it if you’d link to ’em in the comments.