If the US army leaves ALL Americans should leave (= major oil companies), unless they are asked by the Iraqi people to stay.

Personaly I don't consider leaving NOW is a good option. Iraq will become an even bigger mess, with warlords etc. I think the Coalition forces should first repair the infrastructure they have destroyed (if they haven't already) and make sure there will be elections. Maybe all this can be done before the end of the year. Not properly maybe, but it's better than leaving tomorrow. When you invade a country you have certain obligations towards the people of that country, if you like it or not.

I think the best solution is to replace the US and UK troups by arab troups, preferably arab UN troups, and let the US and the UK pay for a huge part of the costs, since they started this mess. It won't happen, I know, but maybe it will help.