I agree, Quatermaster is sometimes miss-played, but now and then it does the right thing.
And yes, Murlock Knight can snowball out of control. For 2 mana (inspire) you get the 1/1 knight and a random Murlock. If you get the charge Murlock, it's a free trade. If you get one of the Murlock buffs, it's insane. And sometimes you get another Murlock Knight, hahah. So funny when that happens.
Murlock Knight is strong because it forces your opponent to react to it. It either wastes one of their removes (ie: fireball or something), or it starts to snowball. Very handy either way. The more removals you waste mid game, the less they have to take out your Boom/Tirion. Another reason why I still like Sylvanas.