The problem was Adsense was hammering my pages with local ads that have nothing to do with the content on my pages, which is a very poor user experience.
This is 100% Adsense own doing, I run evergreen sites where my content will last for years, Adsense earnings were up 4x year over year for most of 2013. The past couple of months Adsense earnings & CTR both dropped & I know it's because Adsense is pushing local ads so hard.
What's funny is Adsense sent me survey asking how they're doing (perfect timing), I'm sure they won't like my answers If they actually read the survey.
I still have an active Adsense account but I'm not running any Adsense ads as long as they're going to deliver crap ads to my pages. Really I doubt If they'll lay off the local ads considering mobile is getting more popular every day.