Same here. Since sept 19 my AdSense CTR (and earnings) have all but completely gone. It's quite devastating for me. I've done a lot of tweaking since then, but that didn't help.
Currently my CTR is down to a completely ridiculous 0.12%.
A large part of my income has simply vanished. And none of the alternatives I found are viable. I tried chitika, and that does give me a better clickrate, but the revenue per click is laughable: yesterday, for every 10.000 impression, I earned 4 cents! Really, people?
By the way: I did notice clicks and earnings appearing and disappearing; G is suddenly definitely shaving off many clicks off my account. Can't think why, I've always been very careful to follow the rules, even though G seems to change the rules in any way they please.
Very, very frustrating.