How have your earnings performed since the introduction of site preview?
About Nov 9th. Google introduced "site preview". From Nov 9th to the 14th I saw a steady decline in earnings as the "previewed" pages were crawled. Since that time, earnings have been down consistently 45%. Impressions are down 5% to 10%. Part of the impression and earnings downturn is certainly seasonal. It's quite possible only a few sites are unlucky enough to see this downtown. I believe the slower the site's response time, the less likely the BOT was to render Adsense ads.
Adsense TOS stipulates that BOTs should never be used to create ad impressions, but clearly Google's Site preview is generating plenty of ad impressions when they record snapshots of pages, which they seem to be doing fairly frequently. Advertisers must be charged for the CPM impressions by Adwords as well.
It seems likely to me that these BOT generated impressions are triggering a smart pricing filter certainly for CPM ads. Poof down go earnings.
I sort of like Google's preview feature, but they must do something to block ALL ad rendering and not trash the appearance of the website either. I realize I can turn of the "snippets" with a meta tag, but, no snippets would probably really cut traffic. I hope Google doesn't feel they have the right to render ads using a BOT, its basically theft of services, render the site maybe, but someone else's ads?
Seems to me it's up to Google search and Adsense to rectify this issue (Mainly Google Search). Then it seems they own Adwords users a refund, Hmmm... and Publishers will need a Holiday Compensation Bonus.