MeHere is a PC app that gets input from a GPS device and serves it from the localhost in a variety of formats that other apps can then use to display your location in realtime. It works for Google Earth but also a whole range of mapping sites with Greasemonkey. Several scripts are already available, but anyone can make their own.
In Google Earth, each GPS device can be tracked simply by creating a network link that refers to the KML file published by MeHere. Many devices can thus be tracked simultaneously.
There is also a forum for help. This piece of free software looks very simple and developer friendly, which should greatly aid its adoption throughout the Web 2.0.