Since the launch of the captions features for YouTube videos in last august, YouTube allows user add captions to one of your videos by uploading a closed caption file using the "Captions and Subtitles" menu on the editing page. This feature is used for people using other languages and even who are deaf or hard of hearing.
Take a look at what folks are doing with online video. I was blown away by the idea and excited for those that clearly are enjoying a medium that is a perfect communication tool for them.