tedster - 6:36 pm on Sep 16, 2011 (gmt 0)

since the Panda is supposed to select the best sites for visitors, I wonder why do they need human reviewers on top of that. If a site is good enough to rise to the top, what justification is there to manually demote it?

Panda itself does not use human reviewers to assign its demotions and promotions. Human reviewers did create the seed set that started the machine learning for Panda, but now it runs periodically as an automated algorithm. Then its output gets integrated into the overall algorithm scoring, applied on top of all the factors that are already in place like relevance, authority, PageRank, etc.

About your second question above: Sites can "rise to the top" by finding and leveraging loopholes in the overall algorithm - because any algorithm can be subverted, that's inherent in a machine algorithm of any kind. Also, as I already mentioned, Google has been using human reviewers to quality check the algorithm's output for quite a few years.

I'm not saying something new and adversarial isn't going on with Google. But I am saying it's important to understand how the rankings are being created before forming opinions and theories.