I would guess some thing along the lines of a Jihad would break out. Whats your .02 on it OT?
It's a complex issue. Generally, Iran is not liked in the region since the majority of the people are Sunni while Iran is Shia'a. Iran already blames the gulf countries (mainly Saudi Arabia) for the American dominance in the region and they have hinted more than once that if US troops used Saudi soil to initiate the attack that they will burn Saudi Arabia down.
What you are essentially looking at is WW3. Unlike Iraq, Iran has the military power, and the US administration made a big mistake and now they realized it. When they took down Tailban (Sunni), they appointed Shia'a in their place (northern alliance). When they took Saddam and the baath party down (mostly secular) they appointed Shia'a in their place. Hizbollah are also Shia'a and they will be a a good point of attack on Israel if a big war breaks out.
The Shia'a power has grown a lot in the region since 9/11, and this served no one but Iran. Unlike Sunnis, Shia'a usually have a religious obligation to Iran, wherever they are (this includes Shia'a in all the countries in the region, pretty much all the countries in the region have Shia'a varying from minority to almost-majority).
Imagine a war like that, the price of oil would probably reach something rediculous, and the world supply of energy would be hit very hard.
China would not be quite about this because this would give the US a huge edge over them if they controlled something like 90% of the world oil reserves.
The biggest losers in this whole ordeal would be us the people in the region, as this is happening on our own land and it is our people who will suffer (yet again) because of another war.