Google has started serving ads through the Google Maps iPhone application, according to SEL.
The ads themselves look rather unobtrusive. When you perform a search, sponsored results are generated from your keywords. These results are denoted on the map by a different pin.
In list view the sponsored result is highlighted in yellow and clearly says sponsored link.
This change comes after a recent report that Apple purchased mapping company Placebase in order to possibly replace Google Maps on the iPhone.