In video, your failures are magnified. As with text it comes down to quality, taste and respect for the viewer. The default in video is poor quality because poor quality is easier to make. Screencasts can be much more powerful than text, after all you have more tools at your disposal - you get to play with audio and the pictures move. The trouble is, to make great video you have to think very carefully about how you want to convey your message. How tight is your delivery? Is it well edited or can I hear you breathing into the microphone? Most people are terrible at delivering on even these basics of video. For people who respect the medium producing screencasts can be time well spent. Consider that there are right now myriad untapped markets on the web in which you can teach via video and charge for quality downloads.