This is the hidden Gem of Google Earth.  
Adding a "Network Link" allows you to fetch KML data from remote servers. It does this in two ways, Time Based or Location Based. So *anyone* can add dynamic data to Google Maps.  
For example:  
If there was a cross country car race, and the cars were equipped with GPS and data fed to a server. You could request that data once every 30mins and, if provided in KML format, it'd update Google Earth with the locations. Photos of the cars or current locations can be used as the icons.
Bud Tugly: Hey. This post got credited in this blog.  
(click where it says "[via]")