So I accidentally clicked on Google's magnifying glass (Web Preview) after doing a site:www.example.com search of one of my sites, AND, I saw Adsense ads being displayed in some cases. Mostly the ad locations are simply white'd out, but not always.
So Google may be doing scripted crawls of our site's actually executing javascript (by accident?) and displaying ads in the Web Previews.
This could certainly be increasing ad impressions enormously! A topic of another thread.