LatLong, Google Maps' blog announces the ability for anyone to edit places information and move markers:

"You can even mark that a business has closed to save someone an extra trip. Of course, we've taken steps to help protect accuracy -- for example, you'll still be able to see the original listing information along with the history of changes made. [...] Beyond editing existing information on the map, you can also add new places. If you search for a business, a landmark, or even a point of interest that doesn't already appear on Google Maps, you can add it for the world to see. Within a few seconds, your addition will be searchable by everyone."

Versioning UGMC (user generated mapping contents) is a good thing to have, certainly.