I recently discovered a site that was stealing content from mine. I'm fairly certain the content is being collected via the RSS feed, so I made a plugin that can insert copyright information at the beginning of each post in the feed. If anyone thinks it might be useful, it's here: http://wordpress.org/extend/plugins/soj-tag-feed/
It's very basic right now, and there's a lot that could be done with it. I'll probably be expanding it in the future.