If I may be so bold as to highlight a snippet of a comment left by Brian Flood on James Fee’s blog regarding those Google Earth ads:
This is AdSense not AdWords we’re talking about here. AdSense allows individuals to share in the profit. AdWords is primarily for the main Google Search page. So as a publisher of data, you could *choose* to place AdSense keywords in your KML and share in the click-through revenue with Google. […] This is something that could actually improve the quality of data, that is, shared ad revenue could help offset the cost of collecting/maintaining some datasets.
If this is turns out to be correct (and I suspect it is) it would make absolute sense (with hindsight), as the recurring metaphor for Google Earth is that it is a browser, with layers published to be rendered by Google Earth akin to websites published to be rendered by conventional browsers. And in both cases, it would be the content producers whom Google gives the option to show Google ads if they feel the need to be rewarded for their efforts.
In which case, the revenue model for Google Earth changes slightly. Sure, you can still pay upfront to remove all ads, but in other cases, Google shares its revenue with content producers, which spurs content for Google Earth, which in turn spurs its use. This is even more sophisticated than the Opera model.
And it has the potential to be quite devious too. Imagine a content producer who has enabled AdSense ads for his network link showing the 50 nearest casinos for a given view. Imagine ArcGIS Explorer being able to render KML (it will). Will ArcGIS Explorer then render the AdSense ads that come with the casino network layer, or will it choose to ignore them? Show them, and Google makes money while ESRI serves the base data and foots the bill. Skip them, and the content provider makes no money. Might ESRI rip out the AdSense ads and place generic ads elsewhere to pay its own bills for serving the base data? Would this be legal?