Boons makes some good points below. I'll add just one thing: In his two and a half years in office, Ban Ki Moon has generally eschewed the kind of moral grandstanding that earned his predecessor Kofi Annan great respect in some quarters and enemies in others.  Instead, Ban has opted for what he calls "quiet diplomacy" that generally involves direct, private consultations with the world's worst leaders in order to secure certain concessions from them. Sometimes this can work, other times not.   Shortly after cyclone Nargis hit Burma, Ban met with General Than Shwe and convinced the junta to open Burma to international humanitarian agencies.  On the other hand, Ban came up largely empty-handed after his most recent trip to Burma to urge the junta to release Aung San Suu Kyi.  

The point is,  the Secretary General of the United Nations is not a position with much real leverage or power over member states.  To the extent that Ban can exert some leverage in negotiation it is because he has the backing of the Security Council.  But in situations in which the Council is divided (as in Sri Lanka and Ban's second trip to Burma) the S-G's hands are pretty much tied. There is no way he can back up tough talk with tough action.   This is something that should not be lost when discussing the job of the Secretary General.