YouTube publishers will need to be aware of a rather arcane legal aspect of the Terms of Service issues. YouTube can take down allegedly infringing videos for copyright under DMCA Safe Harbor, of course, but it can refuse to restore a video where a normally legitimate counterclaim (including Fair Use) is made, if YouTube has a “contractual obligation” to the original content owner.
The relevant case is Lenz v. Universal, which Amul Kalia explains here on Electronic Frontier Foundation, here. Note that the video in question can still be viewed on “Liberal Viewer” here.
This problem has not been reported much outside of EFF, but Michigan Standard has a story on it here.