Marc Leibowitz, director of strategic partnerships at Google, speaks on revenue sharing with Adsense Publishers.

JenSense recently quoted a NYTimes report on Shawn Hogan that says Google pays Adsense publishers 78.5 cents on the dollar as revenue share.

The NYTimes report author Bob Tedeschi derived the magical figure 78.5 from the latest Form 10-Q given in the SEC filings.

Though Google has never officially disclosed details on revenue sharing, Redmond Report points to a FolioMag story where Marc Leibowitz, director of strategic partnerships at Google, speaks on Adsense Publisher cut:
As a rule, Google pays out 50 cents of every dollar to partners - and can range up to the full dollar, depending on the size of the relationship
Marc quoted this figure while responding to reports that Adsense publishers revenue from the Google’s AdSense contextual search advertising program seemed to decline.

Marc also said that Google is making a concerted effort to weed out “made-for-AdSense sites” from legitimate publishers, “We invest heavily in mechanisms that distinguish bonafide publishers from non-bonafide publishers,” he says. “It’s like a game of cops and robbers. As soon as you have a certain set of techniques to police this distinction, the bad guys figure it out all over again.”