Do you guys think they ran it on April 11th and May 6th or just added new penalties?
I am beginning to think it's like Page Rank on the toolbar. Algorithmic but run when Google decides and at different intervals. The only difference is that there's no 'internal page rank' that updates daily in this case, you're stuck with the score from the last time. Google probably did the PR thing to stop SEOs from seeing their PR go up as they got new links. The same principle could apply here, even though many just did what Google said it's Ok to do, and got penalized.