Sgt_Kickaxe - 2:43 am on May 10, 2012 (gmt 0)
Additional information: The number of clicks from 'web cache and other' has quadrupled since adding the last site. I do employ the whitelist in adsense and so I have earned nothing from the new surge in web cache hits but I shudder to think what might have happened to my EPC if I did not whitelist. All of this has me thinking a competitor can indeed cause your overall RPM to drop if they include your adsense code on some spammy sites.
I'll report again if there is any change, for better or worse.