TypicalSurfer - 12:44 pm on Sep 8, 2012 (gmt 0)

It looks/feels a bit like there is some stream processing going on, of course going down that road of thinking would violate the strict "delineation between adwords and organic" mindset and assume that google is indeed tweaking their system for profit.

Say you take x amount of revenue queries and return results from index "a" until revenue targets are met (this could literally be on a sub-second basis), when target is hit send those same/similar queries to index "b". The possibilities are endless with this but would certainly explain what appears to be "random", you'd really have to look at this from a revenue shaping standpoint vs. traffic shaping.