Back in early May I had 3 messages from Google Adsense warning about 3 (old and forgotten) sites in contravention of Webmaster guidelines.
I immediately removed the sites completely and parked their domains.
It appears to me that since that point I have been allowed to continue without an Account ban but my earnings dropped considerably. Subsequently, they've also been dented by Penguin 2 but there is a definite window just after the contravention letters where things have gone downhill. One symptom is that the relevancy of ads served has deteriorated (almost as if I'm now served some 2nd tier advertising).
I'm aware Google stated some months back that they wouldn't necessarily Ban accounts but work with Webmasters. I wonder if, at the same time, they have introduced some kind of degrading or probation for those allowed to continue?