YouTube taking down content in response to notices of infringement. (Down comes John Stewart, Colbert Report, South Park, etc. at the request of Comedy Central.)
MySpace works with Gracenote to detect and block copyrighted materials. (This is actually in addition to the DMCA at work. Under the DMCA, MySpace must respond to notices of takedown. They are not required to affirmatively search for and take down copyrighted materials, absent a notice from the alleged copyright holder.)