Robert_Charlton - 5:24 am on Jun 12, 2012 (gmt 0)
I have to believe that some sort of throttling is occurring using how many times a url can appear in the serp.
Perhaps related... I'm guessing that the recent rollout of search refinements (at least that's how I see it) might also lead to testing that we could see as some form of traffic shaping.
I don't know whether the type of refinements Google is testing will produce easily observable patterns, but see notes here on what I see the Sitelink type refinements being tested are likely to be....
Host Crowding vs Brand Authority
I'm initially, at least, not seeing localization effects in the searches, but I performed only very cursory searches and location changes to check that.