The latest beta of Google Earth 4 includes a feature previously available only in the paid versions: drawing tools. "The path and polygon drawing tools are now available in the free product. You can easily sketch figures on the imagery for richer annotations and can share these overlays as KML or KMZ files."
You can use these tools to mark some regions on the map.
There's also a way to measure distances between two locations and the length of a path. Just click on the ruler, define your path using the mouse and see the distance.
The latest version of Google Earth is
available here.
