The homepage of our our sites dived about 7-8 spots in mid-march. The homepage was ad-heavy (the sub-pages were not and weren't affected). However, since this happened mid-march, is it safe to assume that this would be too late to be an above-fold content penalty?
Also...how on earth does google know the difference between an ad and say glorified navigation button or picture? Are they parsing known link profiles? There are flash sites we keep an eye on as well as wordpress sites with mega slideshows at the top...they weren't hit.
I'm almost thinking this algorithm thing is a ruse..and google is using EWOQ or a similar human review team to determine whether a site it too ad heavy or not. This would also explain why many sites haven't bounced back yet...the human reviewers haven't got to them.
Or perhaps it is a combination of the two... Googlebot flags a suspected ad heavy site for human review and the humans actually assign the penalty.