hyperkik - 4:48 pm on Jan 11, 2006 (gmt 0)

I suspect Google imposes a smartpricing "credit limit" - sites are trusted to a point, based upon traditional traffic patterns, but if their traffic suddenly surges past their "pre-approved smartpricing limit" then smartpricing kicks in until the limit is increased (either automatically when Google finishes crunching its data, or manually by an AdSense employee).