My CTR has dropped and I reckon it is because the ads are more often than not irrelevant. Have you noticed anything similar?
My CTR was good a month ago but it dropped drastically very low and i am not getting good income from adsense now.
What I have observed for the past few weeks is that the topics that I usually search for, or the niches of the sites I usually visit are the ones that are showing in the ads and not the ones actually related to my content. So, for example, today, I will update and post contents in my real estate site, therefore making lots of impressions on it. When I eventually visit my law site, the ads on my law site will still be real estate. This is the job of the cookies dropped I guess. So people who do not clear their cookies often will most likely have the same category ads appear over and over again.