freejung - 5:12 pm on Aug 19, 2011 (gmt 0)

Google engineers have mentioned "ads dominating a layout" so frequently that I cannot doubt this is in play.

Yeah, and right after Panda 2 the Adsense team changed their layout guidelines. That was pretty much a dead giveaway.

On the other hand, I changed my layout to feature content much more prominently right after that, and I think it made the site a lot better, but it didn't help my rankings at all as far as I can tell.

there are a large number of signals

That's the problem, and why I'm skeptical whenever anyone thinks they've boiled it down to any one factor or even a short list of factors like this one. It's more complicated than that. If it were that simple, it wouldn't take so long to run.