OK I'm not saying that just because a site has adsense it gets penalized - that would be foolish, rather that it might be a factor.
I didn't mention in my original post that after Panda 2.1 I developed 4 similar sites but all with unique content. Different hosting accounts. Two had Adsense and two didn't. The two with adsense originally ranked very well but have disappeared with Panda 20 / EMD. The two without adsense have kept their ranking.
Their seems to be a pattern for me - my sites with adsense are now regularly affected by updates. Non adsense sites seem to be unscathed/