diberry - 10:28 pm on Jun 6, 2012 (gmt 0)

@tedster, could we kind of put together a list of the various theories here, and what's wrong with them?

--Maybe Google is trying to force Adwords buying on certain phrases. Some people claim this would be too expensive in terms of computing power and all that; others say it wouldn't.
--Maybe Google is trying to give several equally deserving sites their time at the top of the US SERPs, but it doesn't really follow that the traffic during your not-at-the-top times would be totally useless "zombie traffic." It should just be more mixed.
--Maybe Google is testing different taxonomy profiles to find site niches, but that wouldn't take years.

Are there others? What about specific theories on what this could be an accidental byproduct of? Like, what would the algo be trying to accomplish when, as a side effect, it winds up sending certain sites this zombie traffic?