Valdis Krebs performed a simple experiment. He looked at the “buddy list” on Amazon of several dozen top-selling political books and graphed the results. (Link from BoingBoing.) The result is two clusters, as one would expect, but with one book in the middle, with “buddies” on both sides: What Went Wrong by Bernard Lewis. (Also, arguably, The Clash of Civilizations by Samuel Huntington.)
The “cocooning” controversy could be resolved the same way. Steven Den Beste theorized last year about blog clusters but without data to back him up. So the assignment, for someone less lazy than I am, is to create a chart, after Krebs, for blogs instead of books, using for data the top 100 blogs and, say, the first ten blogs in their neighborhoods at BlogStreet. This would be imperfect but indicative. How many clusters would there be? Who would be in the middle? Do people often read blogs that they disagree with or are blog readers, like book readers, blinkered by confirmation bias?
Peel away all the layers and the Onion would be in the middle i’m betting, keeping the nucleus warm for agendabender.