Here are the some facts from Google’s Q2 2006 SEC Filing

Google made a significant profit (Q2 2006 $721,077,000) and 98.9% of their revenue is from online advertising.  Of all Google advertising revenue 41% (Q2 2006 $996,567,000) was generated by the Google Network web sites which are sites not owned by Google by rather third parties. 

According to the SEC filing, the traffic acquistion cost Google paid their network of sites was 78% (Q2 $785,200,000) of the advertising revenue they raised which leaves Google with $211,367,000 of revenue from their network of sites to pay operating and marketing costs. 

Which leads me to assume/guess:

20%-30% of all Google profit is from Adsense.  This assumes that Adsense makes up a majority of the Google Network web sites and that Adsense operating costs are less than 30%.

Previously people speculated that Google shared 50% of revenue to sites participating in Google Adsense.  Their traffic acquistion costs which is 78% of advertising revenue suggest that they may be paying more than 50%.  Google does have some private deals which could also explain why the traffic acquistion cost is much higher than 50%.

Assuming Adsense is the lion share of Google’s network sites and that Adsense has operating costs of 30% then if click fraud is:

Please remember I am just a simple webmaster who is not into finance or SEC filings.  These are just my personal assumptions and guesses based on what I saw in the SEC filings.  Let me know what you think.