If you have a compatible GPS device, recent versions of Google Earth Plus and Pro allow you to track your movements as they occur. For example, you could track your travel progress in a plane or in a car with a GPS device connected to portable computer with Google Earth. Of course, imagery in Google Earth depends on an Internet connection. As a workaround, Frank Taylor of Google Earth suggests that you cache your imagery of your route before departing. Learn more about caching.
Like the time slider, it will be interesting to watch how Google Earth users apply this feature. I can envision live blogs of treks that use network links that describe interesting journeys that individuals embark upon.
Learn more about realtime GPS tracking.