I've posted a few times about how two of my three simple, HTML content based sites got slammed in Panda, and one had a slight gain. Try as I might, the only differences I could find between the three were the age (the unaffected site is the youngest), the level of infringements (the youngest sites has been largely untouched), and the subject.
I was reading the WebMaster Tools thread today and saw a post by a large magazine publisher, I'm not sure if we are allowed to use names here, but they publish a number of high quality magazines for do-it-yourselfers and wannabes titled "Fine ______". According to the Webmaster Tools post, two of their sites have been impacted, the remaining eight or nine are untouched.
As near as I can tell, the platform and structure of these sites is basically identical. Same layout, same ad programs, same forums, etc. The main difference I see is with the subjects.
When Google say 11% or so of queries have been impacted by Panda, is it possible they chose a few subjects that are notorious with article farms and only applied the new filter to them? And if the results of the filter looked suspicious, penalized the whole domain, even when the domain included much more?