It would seem that the easiest way for everyone to always have the updated placemarks would be to create a single KML file with embedded folders (eg restaurants, shopping centers, hotels, etc.). Store that KML file at
http://placemarks.koratfarang.comThen create a small KML file with a <Network Link> tag that points to the URL of the complete KML file. That way the placemarks are dynamically updated each time the user logs on to GoogleEarth and then periodically while they are logged on. This eliminates the need for each user to download every time a placemark is added or updated.