The new version of Google Map Maker lets you submit updates, edits, or other changes to a map—and once it’s approved, you’ll see your additions on the live Google map.
…With the redesign, you can add currently unmarked hiking or biking trails, rivers, or ball fields, and update existing buildings and landmarks by drawing your addition directly on a map. In this way, Google can rely on your map updates to essentially crowd-source its maps.
Changes will also appear on Google Earth. As they say here, spam will always be a problem. You can guarantee that someone will manage to use this system for wholesale spamming that will work for a while. Don’t be surprised if the crowd-sourcing (ie free data) gets turned off one day.