DeleteCity saves videos from YouTube deletion.
DeleteCity adds 2 scheduled tasks to your WordPress blog (you can use the CronView plugin to see them http://wordpress.org/extend/plugins/cron-view/): the caching task and the posting task. You can change the frequency of these tasks under "Delete City Settings".
By default, the caching process runs twice a day. It fetches standard YouTube feeds that you supply and downloads each video in the feed to your server using youtube-dl. It notes the time that it was downloaded, as well as the title, author, and other properties. The next time the caching process is run, DC checks back to see if the video is still available. If it has been removed, the video is marked as "removed".
To save hard drive space, videos are automatically deleted after 3 days (customizable in Settings) if they are not found to have been removed.
Once a week, DeleteCity will post all of the deleted videos it finds to your blog.
As shown below in the TO DO section, future versions will optionally email the author of the videos and invite them to come back to your blog and comment on why the video was taken down. It will also (optionally) submit deleted videos to a central database that will be made avaialble to the public.
youtube-dl is a 3rd party script for downloading YouTube videos. You probably shouldn't use this directly - it is called from the other scripts. You can find out more about it here: http://rg3.github.com/youtube-dl/
Good question! It is unarguably a niche plugin, and not terribly practical.
Let's just say that this readme file isn't the proper place for that topic. If you'd like to discuss it, I invite you to email me at jeff [at] crouse [dot] cc.