Can someone here please enlighten me on what threat exactly Saddam Hussein poses to the USA? I have never heard it articulated convincingly by anyone who can produce any supporting evidence.

Even if he does have nuclear or biological or chemical weapons (and on nuclear the UN inspectors say not, on chemical/biological they say "not proven") how is that a threat to the USA which is many thousand of miles away from Iraq?

There are a number of countries out there which have more capability to threaten world peace (either directly or indirectly) including North Korea and Israel. There are also a number of countries posing a more clear and immediate threat to their neighbours, particularly in Africa. Moreover there are many countries ruled by a regime which an objective observer would not say is in the best interests of the bulk of that country's population (again, much of Africa, Iran, Libya, North Korea, some of South America, much of ex-Soviet Central Asia).

If the USA feels the need to be the policeman of the world (which is debateable) I can see a number of things that should be higher on the priority list than Iraq.

Just to be clear, I do understand the threat posed to the USA and many other countries by Al-Qaeda, and I have no problem in principle with the invasion of Afghanistan or other actions against Al-Qaeda (although I am beginning to get concerned about the fact that Guantanamo Bay is apparently outside the jurisdiction of any country). But that is an entirely separate question, and I have never seen any evidence linking Iraq to Al-Qaeda any more strongly than many other countries (and being a secular state it is much less strongly linked to them than most Muslim states).