A WebmasterWorld thread calls attention to a recent PC World article that states that Google will soon integrate AdSense into Google Maps, "meaning some push-pin graphics used at the maps site could be turned into mini-advertisements."
This has not been rolled out to the public yet. However, in the proposed implementation, a hotel can use a specific icon instead of the traditional push-pin design to increase visibility of the location on the map.
When launched, users will have "complete control" over what will be visible to them. They can turn off these sponsored results. Forum members suspect that this will be turned off indefinitely, so perhaps that won't be a long-term solution for Google.
Forum discussion continues at WebmasterWorld.