lammert - 4:37 pm on Jan 29, 2010 (gmt 0)

Cleanup on the AdWords side can have visible impact on the AdSense side is my personal experience.

I was hit in July 2006 by the update of the Quality Score algorithm to push MFA sites out of business. I wasn't an MFA myself, but as AdSense publisher my income dropped 40% because there were much less advertisers to fill my ad slots and EPC tanked accordingly. EPC stayed stable since that period within +/- 10% and is now slowly climbing again.

More reading on that 2006 AdWords update: [webmasterworld.com...]