Love it or hate it, but the UN is needed as a forum between the nations on this planet. It is for sure not a place of morale, but it is a good place to communicate. Even the standpoints of the pariahs like Iran or North Korea can be checked through the UN without any problems.
I doubt that the UN has the justification to play the "world representation" or the "world sheriff", since there is absolutely no democratic basement. Anyway some achievements like the standards on human rights, justified or unjustified war etc. are not bad.
If the US are lauching an "alternative" they only would have the backing of their traditional allies like GB (maybe yes maybe no - maybe Jimmy maybe Joe - hehe), Australia and several smaller countries. America would isolate itself, since it still doesn't represent the world alone.
I think that we rather need a debate over the duties and responsibilities of the UN. Bolton is right - we have to fix the institution, but he shouldn't forget that the world doesn't consist only of friendly nations. It is unrealistic to declare a "pax americana" as long as America has not the means to deal with all those thugs alone and immediately. During the Iraq crisis America proved that it can handle its problems alone, although the discussion with the other nations was more than painful. Unregarded the fact that there was no consistent international backing for the Iraq war, the debate helped to show the new political realities after the cold war. Furthermore it showed the weaknesses in the system of the West. What is i.e. the NATO worth if not all members will stand in for their duties? What has to be done in Europe? What are the new focuses of power (China, India?)? What is the American role in the future? How can old constallations (France, Germany) be restored?
It is better to have a organisation that reflects the real world and its disabilities than a congregation of false allies who will backstab the only remaining world power as soon as they can.
If all that's needed is a forum to communicate, then just outsource its function to a corporate meetings planner.
Have a UN meeting four times a year at various locations around the world.
We don't need a permanent, entrenched bureaucracy with arrogant aspirations to being the world's highest government authority, and the power to levy taxes, raise armies and control the Internet.
The only thing worse than the UN's ineptitude is the horror of having it be empowered and efficient.