U.S. District Judge Louis Stanton in New York today said YouTube wasn't liable for infringement.
More here (along with the actual ruling itself):
This still preserves the very flawed "safe harbor / take down notice" regime which has proven to be subject to abuse and various end runs around fair use principles, so this hardly a game changing development. But it still would have been far more disastrous had the decision come down in Viacom's favor. In that aspect, its a small step in the right direction.