On Youtube, takedown notices are issued on a regular basis. Most of these are issued for copyright violations, and most are responded to as such. The RIAA and MPAA are at the heart of these takedowns. But now the Department of Homeland Security is involved, and things are getting tricky:

http://fromthetrenchesworldreport.com/homeland-security-issuing-its-own-dmca-takedowns-on-youtube-to-stifle-speech/18742/