I find the site that has dropped all rankings from google providing a higher CTR in adsense than when google is the biggest referrer. When Google provides most of the traffic, the CTR is actually lower. So yesterday and today, when the traffic has been way, way down for this site, the CTR has actually been better.
Not surprising. I recently got analytics going and it turns out that visitors from google have the worst conversion ratio. Yahoo traffic is much better and direct access even better. Some of the best comes from targetted links and some of the worst from untargetted links.