Using the YouTube API and the Google Earth API it is possible to synchronise a video to the Google Earth plugin. In other words it is possible to create a Google Earth tour to illustrate a YouTube video or it is possible to create a video to provide a narration of a Google Earth tour.
I've created two examples:
I think this idea has a lot of potential. One way in which the idea could be used is by geography or architecture lecturers to create a Google Earth tour and then video and synchronise a narration of the tour. I'm sure that other developers will think of more applications for this idea.