Has anyone seen a correlation between your ranking in the google serps for terms that relate to adsense ads and your cpc for the adsense ads. ie. as your position in the serps go up, the cpc increases along with your number of visitors.
I have a site that just went from ranking in the 200s for my main keywords in Google, to ranking in the top 5 for the same keywords. During that time my earnings did not change (other than from the increased traffic from G). I think this is a case in which the same thing randomly happens to a lot of people, but is just a coincidence.