I thought I was the only one affected this month. I suggest that GOOG has cut our share down as its stocks seem to be only increasing. Recession is ruled out for now. That should have affected us a few months back.
Partly because of the recession but also it seems to me that people are becoming more ad blind, which is probably a longer term change in user behavior. GOOG is also reducing TAC (traffic acquisition cost) by changing how they display ads, videos and organic results on search pages also. None of this is helpful to publishers unfortunately.
I think its like bsd13 said - people do not want to spend money so just like they aren't at the car dealer shopping for a new car or going to the store to purchase stuff they aren't clicking on Ads as much. Hopefully as things eventually recover with the world economies people will begin clicking on Ads again and advertisers will bid up the prices ... hopefully!