deadsea - 2:42 am on Dec 31, 2012 (gmt 0)
There are many sites that get 80% of their traffic from organic Google (mine included) that were not hit by penguin.
It would be an interesting algorithm to base what percent of traffic a site may get from organic google based on its CTR, bounce back rate, and other usability metrics.
On the other hand, I wouldn't expect them to test it all at once. They do tests all the time where the promote or demote a site for a query to test user reaction. They can do those tests query by query, user by user, and for the most part webmasters are none the wiser.