Shatner - 9:44 am on Apr 16, 2011 (gmt 0)
Weird, I am looking at mirror.uk right now and I don't see any "this is an ad" label on most of their ads. or do you just mean the ones inside the articles? Because the 728x90 and the 160x600 ads for instance aren't labeled at all.
If you just mean ads mixed inside content then that's different.
However here are examples of sites which were NOT hit which don't follow your rule:
They have ads inside their content on their posts and do not label them at all.
But they weren't on the winners list, just no on the no effect list.
I can find lots of "no effect" sites that break your rule, but you're right... on the winners list all of them either do not have ads in their content, or they have in there but clearly label them as "ads".
On the other hand many on the losers list have ads inside their content, and do not label them as ads.
Genius brinked. I think we may have stumbled upon the very first, confirmed Google Panda factor. It's obviously NOT the only one (which is probably why some sites have no effect even with this) but it definitely seems like this could be one of the factors.