As reported on Google Earth Blog, Ogle Earth and elsewhere, Google today launched a new service for Google Maps whereby anyone can mark up, draw on and annotate a map directly within the Google Maps interface. It is very cool and super easy to use. You can read the user guide I wrote for this new service, which is called My Maps.
This relates to Google Earth because once you have created you map, you can export it to KML and thereby view it in Google Earth. After you create you map, click the KML link to download a KML file that contains the content you've created, then open the file in Google Earth.