aristotle - 1:12 pm on May 29, 2012 (gmt 0)

I have limited data to go on since none of my personal or other clients sites were effected by penguin.

How do you know that these sites weren't affected? If, as you say, many spammy pages have been de-indexed and their links devalued, then it seems to me that this would cause a "chain reaction" that would spread the effects throughout the web. Some sites may have been effected only slightly, and some of these may have even gained in the rankings as other fell, but I doubt that many sites have been totally unaffected.