Surprisingly I haven't noticed any significant changes on my sites
8.5%? That's not so much.
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I guess the big question is what is their trend for the next month right? Does the trend keep dropping or is sufficient Google damage control conducted offline to repair the damage...
Just makes you wonder what offline relationship Demand Media has compared to Hubpages and the others who got targeted.
Hubpages, I have no idea what the issue is.
The Farmer update is supposed to rank sites with higher quality content higher and sites with low quality content lower. The question is how Google is determining the difference between low/high quality content and are they using human evaluation?
Google does have human evaluators. You can find some interesting tibbits here.
I guessing that Google is using some combinations of trust rank (some human evaluation) and types of inbound links to score the quality of a page. As you said, human evaluation would be time consuming. So only some sites would have human evaluation.