I have released a small update to the mythnettv code I maintain for myself. Besides some other changes I have made in the last few months the latest addition might be of interest to those who want to import YouTube videos into the MythTV Recodings screen. You can get my copy of mythnettv here and make sure to read the README file as many new exotic dependencies have been added differing from the original code made by Michael.
To sum it up, you can now take a link like "http://www.youtube.com/watch?v=WdU-UtEJEIA" and download it into MythTV. Or you can take a RSS feed like "http://www.youtube.com/rss/user/AtheistFoundation/videos.rss" and subscribe to it.