Well, the honeymoon is over. Disguised Toast has already found a game breaking-ish bug in Hearthstone: Whispers of the Old Gods. Using Fandral Staghelm, followed by Dark Whispers, players are able to attach taunt to the face of their hero despite the fact they are not minions. When a character tries to attack...they can only deal face damage and cannot touch minions!

I don't necessarily consider it incredibly useful as a typical late game 10 Mana board will not be as empty as this, but it could be a problem none the less. See it in action below.