tedster - 11:17 pm on Dec 9, 2012 (gmt 0)
The date (November 22) may be important. Nov 21/22 was when "something" happened, most definitely. We had decent buzz about SERP changes in our monthly update thread and later learned that Google confirmed a Panda Update [webmasterworld.com].
But that wouldn't explain why you see EVERY site in your 200 site portfolio being affected. Statistically, it seems way outside any accidental correlation. Panda is supposed to be aimed at site's whose content is not actually spam, but not really good quality, either. The Panda algorithm is a response to content created merely to rank (content farms e.g.) rather than to be of value to visitors. However, they have had a lot of trouble with sites that are scraped - choosing the scraper to rank rather than the original content creator.
All that said I still can't see how a Panda Update would affect all 200 sites at once - created by different owners, with different amounts of time online and on different topics. Does not compute.
Like cabbie, I have supervision of WMT for a good variety of sites. Some were clearly penalized before they came to me, some got the "unnatural backlinks" message but only a portion of those lost search traffic, and others are truly thriving and setting new records for themselves. So I don't see that using the standard way of sharing WMT accounts creates a situation where the whole portfolio is penalized, either.