edinburgher - 9:07 pm on Mar 14, 2013 (gmt 0)
My hypothesis is that when they rolled out this change, they hit the RESET button on the targeting statistics and its going to take time for googles engine to re-learn what ad's to put on what sites again.
I think you're probably right. And I can see why it might be necessary if they're introducing a new factor into the algorithm. But why on earth can't Google just *tell us*?