I couldn't test this myself, cause I was stupid enough to give the quest back to the Questgiver.
So today on EU there is new capaign Quest.
You have to talk to Thrall in your Garnision and he takes you to Drek'Thar or something.
At the end of the campaign you fight against an big Elite and you get a Buff that gives you 600% increased damage for 1 minute.
Not only that, you can stack it up to 1200% damage for 60 seconds and so on.
So I basically gave that quest back, but I killed a normal mob with this buff, so you might be able to carry it around ( Dugeons / Raids / Arena )
Someone could test that? :P
Sorry I know only exploits here, but I really thought that this could be a very very big one.