My ctr was steady for many years and has also dropped by ~60% in the last couple of months. I believe personalized search may have something to do with it. Obviously, if your site is about cars and your site is displaying underwear ads beacause your visitor was searching for underwear just prior to coming to your site, the ctr will be way down because the ads don't fit well with your content.

I have also seen a recent fall in CTR.
However, unlike Surfer67's "personalized search" issue I believe my reasons are more to do with 'geographical targeting'.
My site covers 'Widget Services' in 'Geographical Area A' and for several years 90% of the Google ads consisted of 'Widget Related Services from Area A' and produced a healthy CTR but more recently at least 50% of the ads are for 'Widget Related Services from Area B or even C'and this has resulted in a decreased CTR.
I'm hoping that this is just a 'temporary' glitch and that things will return to normal.
After all it is no-one's interest to have this poor targeting - I lose out, Google loses out and I imagine the Adword campaigns will not produce the desired result.

unlike Surfer67's "personalized search" issue I believe my reasons are more to do with 'geographical targeting'.

Initially, I also concluded that it was geographical since I run a tech site and a good chunk of my traffic comes from India. I had concluded that the Indian traffic was either being served public service ads or the clicks weren't being counted. I know believe it's probably a combination of geotargeting and personalized search.

It would be nice to know what ads, if any, visitors from foreign countries such as India are being served. It would answer alot of questions.

I used to have major traffic from the US but this is declining slowly and traffic from India is increasing gradually!

I added a 468x15 in 80% of my content depending on layout.

When I look in the daily average of clicks, I am now back in the range between August and September 2009.

ecpm and ctr were down for months, now after maintance work it is terribly down. can't understand the reason

Maybe you've been "smart" priced.

Happens to the best of us...

for around 30 clicks the the earning it shows is just 3 - 4 USD this is getting worse.... it now feels like adsense is also similar to programs like infolinks

Drop back and punt.

@wyweb, Could you please elaborate sir?