freejung - 7:49 am on Jul 13, 2011 (gmt 0)
For long do you think this will go on once started?
Until they decide that they have succeeded in weeding out most of the spam from most of the high-traffic SERPs. If search quality is the highest priority and computing power is the bottleneck, it would be only after most important SERPs are clean that it would be efficient to start reevaluating previously scored sites.
I have no idea how long that would take.