So, looks like the June thread is here :)
I believe last May, Google has increased their filtering of what it considers invalid clicks, in response to increasing bot activity and reduced revenue from Adwords. The April click bot attacks might have contributed in spurring them to tighten up everything. Even the amounts reduced to finalize the Payable Balance seem to be off the charts (some folks had a decrease of 50%)! If you are seeing a reduction in CTR, I think it's because of a more aggressive algo. Clicks are deducted on the spot now - I've seen it with my own eyes.
As much as we'd like to hope that things turn for the better in June, I think it's probably just a continuation of the trend started in May. What I did was refocus on my sites and slog hard again to make new pages and attempt to gain new visitors/pageviews just to regain lost income.
I've said before and I'll say it again, just to keep up with the reducing revenue from Adsense, everyone is going to have to dig deeper and deeper down the barrel to get more traffic. A lot of RPMs are just going down from year to year. Adsense is dying.
I think my efforts did help one way or the other in keeping May from being the worst month in 5 years for me; it only ended up being the worst month in 2 years, LOL.