This just occurred to me last night.
How long do you think it will be before Google starts tracking sales conversions for it's AdWords advertisers, and starts adjusting payouts based on how well your site converts sales for the average AdWords advertiser?
It would be sinfully easy for Google to institute this. All they would have to do is give their AdWords advertiser an HTML snippet of tracking code that they could put on their "sales thank-you" page, or whatever page they take a visitor to when a sale or some other desired action is completed. They already know the referrer (you) from the AdSense click event.
FindWhat, one of the largest second tier PPC engines, already does this (we use it). They give you a piece of HTML code with a tracking number for the particular PPC Ad your tracking. It allows their engine to trace back to your Ad and get the _search keywords_ the visitor used to get to your site.
Then you can generate a report showing you what your conversion rate is _by keyword_ for your Ad. You can even give them a per sale profit figure so you can track your keywords by ROI (return on investment).
The same method, plus the AdWords referrer URL, would allow Google to do the same for their AdWords advertisers.
So soon you'll have people structuring their AdSense pages to help pre-qualify possible AdSense ad clickers. It will be an interesting ad hoc synergy between webmaster and AdWords advertiser, but potentially a big headache too.
You read it here first. :<o