Effectiveness of the UN...wait what have they effected again? oh, thats right... Nothing.
Put simply, the U.N basically follows this order.
An important topic is brought up. It is debated and discussed and all positive and negative aspects of this topic ( or action) are brought up. Half the U.N is for it, half against it. Then, all the politicians decide that its too dangerous to make any action, because if it is the wrong one, they will lose their nice comfy seat of power.
So, while they may say they discussed things thoroughly, they usually end up at ground zero, with no decision made but to stay out of it.