I have a site based on helping people that's been around since 1997. We've spent the past year testing every possible AdSense ad location and design to find the best performing units. We've also optimized pages to load nearly instantly, and have redesigned the entire layout to match Google's best practices.
(It was A LOT of work. Whew!)
As a result of all this, our CTR has climbed from a .25 average to over 3% average. Today, we're well over 5%. This worries me.
I met for a 1-to-1 meeting with a member of the AdSense team last month. They were very impressed with what we'd accomplished. However, I was told that, if the CTR goes over 5%, AdSense starts getting suspicious.
I notice that our CPC is dropping fast. I don't want to undo the hard work that Google liked so much, but I also don't want to get banned by the automated system.