In the last 7 days I've seem a drop in my RPM (earnings for each 1000 impressions) from about $40 to $25. The CTR has dropped a little bit, and the CPC dropped quite a bit. As I was sure to be Smart Priced, I decided to start showing ads only to visitors coming from SEs. What impresses me is that my CPC is the same now as it was before, even though I expected the visitors from SEs to yield a higher CPC. Now I'm not even sure if I'm Smart Priced, and/or if I should keep showing ads only to SE visitors.
Smartpricing usually hits sites that get visitors but not targeted traffic. Such traffic might click your ads but very few clicks actually end up being profitable for the advertisers. My two cents - focus on your content and try report to Google product forums should you see unusually high CTR, but low CPC.