I speak often about teachers using their interactive whiteboards to create screencasts of curriculum content to publish to the web.  Sal Khan, who created Khan Academy, speaks of his journey into teaching, which started by his making videos to help his younger cousins with their math.  His work has become a sensation.

In this  presentation he speaks a little about how and why he has done this.  He speaks to the format. For those teachers interested in using screencasts to support your instruction with students, watching this video is a must. He goes on to share some wonderful points about 16 minutes into the 22 minute video.  It's worth your time.