We decided last fall to start teaching Python using the IPython Notebook rather than a plain old command-line interpreter. It will take us a few months to complete the transition, but one of the things that we're hoping to do in the meanwhile is build a record-and-playback plugin for the Notebook. We think this will be more useful than the screencasts we currently have because:
People can't pause a video, then copy and paste its text, because there is no text: there are just pixels arranged to look like letters.
For the same reason, the code in videos is invisible to search engines.
We can't diff and merge videos in version control the way we can diff and merge source code and Notebooks.
Video is inherently less adaptable to new platforms (e.g., tablets and smart phones) than first-class content that's rendered by the devices themselves.