davedm - 5:01 pm on Dec 2, 2011 (gmt 0)
We're seeing traffic throttling vary according to the time of day too; massive reduction in organic traffic from Google overnight and during the mornings; and a modest increase during the day and evening.
We've been in the industry 10 years and this isn't natural behaviour, peoples search patterns just don't shift like that.
With regard to throttling traffic in general, Google certainly does this - we have countless examples where organic traffic has increased due to news or other events and then almost exactly the same amount of traffic "been lost" later in the day as if to compensate. Clearly there is a limit to how often a non-Google owned property can "be the best result for users" per day ;-)