tripower - 7:45 pm on Jul 2, 2013 (gmt 0)
We're seeing the same thing. Starting on Jun 30th we had an 80% drop in CTR. Everything else is normal (traffic, page views, ad impressions). The amount of money we're losing is staggering.
We've sent a message to AdSense through their AdSense contact form, but haven't had a response in the last 24 hours.
This appears to be happening to a good handful of sites.
I just wish there was a way to get in contact with AdSense.