In the first paragraph you say that Google keeps 78.5%, but in the second paragraph it says Google pays 78.5% to the people who display the ads.

which way round is it?

Thanks, fixed, this truly changes my complete article :/

Google takes about 20%? Sounds fair to me.

Google's traffic costs for the search part of AdSense are roughly 79% – as reported in last year's annual report. That's what they would pay AOL or the New York Times for AdSense for search placements – 79% of revenue. Remember that AdSense for search is the much bigger part of AdSense, even though many bloggers think of AdSense for content first.

(see here: http://gotads.blogspot.com/2005/03/goog-annual-report-must-re_111229081891402253.html)

However, that doesn't mean that Google 'takes about 20%'. Most AdSense providers get nothing like 79%. For bloggers, Google is probably taking more like 60-70% of the payment for a click and giving the blogger around 35%.

Google can dynamically change the percentage pay-out at any time – and they do.

For most people AdSense is the easiest ad system, so they don't really know or care what Google is paying them.

I really doubt they only take 20 or 30%. I would suspect its jsut the opposite in that they take 70-80%. A simple comparison of adword costs and my CPC in adenses tells me they are keeping the biggest piece of the pie.