Haha, I looked at this thread title and thought my opportunity had finally arrived. Guess not quite yet. But in answer to your question, I would mount a full fair use defense and counterclaim for copyright abuse and violation of anti-SLAAP (Strategic lawsuit against public participation) laws. If the suit came after a DMCA takedown notice, I'd also bring a class action under the misrepresentation clause of the DMCA on behalf of ever vidder whose work they had taken down with improper DMCA notices that failed to consider fair use (which they're legally required to do). Actually the latter part I am seriously considering doing anyway as soon as I graduate from law school and get a little experience as a lawyer so I know what I'm doing. In my view, AMVs are highly likely to be considered fair use (both with the video and the music) if the issue ever went to court, and copyright owners that abuse the takedown process on YouTube by misrepresenting them as infringing could be held liable for it.
At any rate, if you want to read a full blown analysis of whether AMVs are fair use or not, I wrote one a couple years ago which you can read
here.
By the way, that website (
http://fairusetube.org) is something I made to help amateur video editors deal with copyright problems on YouTube. Everyone here could probably benefit by reading my
Guide to YouTube Removals which discusses your options for getting videos restored after they're taken down on YouTube for copyright violation.
~Patrick M.