"After a great deal of unproductive negotiation, and remedial efforts by ourselves and other copyright holders, YouTube continues in its unlawful business model. Therefore, we must turn to the courts to prevent Google and YouTube from continuing to steal value from artists and to obtain compensation for the significant damage they have caused."
Viacom and Google have been in discussions for a while, and many videos have already been removed. Apparently not enough for Viacoms liking. Google has not yet commented on the lawsuit.