Google Earth is probably the first and only desktop application to have AdSense Ads. These ads are is now showing in at least two different places inside the application:
Figure A: When you search for a location or business, the ads are displayed in the search results itself.
Figure B: When you click a placemark (any red pin on the map), the ads are displayed next to the review /address of that location.
Google makes an exception
I find this interesting because Google policies strictly do not allow software developers to integrate AdSense ads in their desktop applications. If that policy changes, we could see more and more of Office 2010 Starter or FeedDemon like applications that are completely free to the end-user but supported by web advertising.