An informative report at Google Developer's blog informs Andrew Eland, Google Maps Engineer in a presentation at Google developers Day 2007 held in London, UK discussed the unveiling of AdSense for the Maps API.
As "The bulk of the talk focused on the newly announced Mapplets." Andrew Eland described the latest feature by saying, " The marker on the map looks slightly different than the normal ones, and when clicked on show a sponsored link. Developers are allowed to chose whether they want ads on the map, and if so how many ads to display. Google created this to allow developers to monetise their mashups, and if users do click through, the revenue for that ad will be shared."
The presentation is available at Google Maps UK.