Iranian invasion
This article in the Seattle Times reports on potential problems if we were to invade Iran, including increased threats to oil lines in the Persian Gulf, Iran's ability to incite attacks in Israel, and futher escalation of the insurgent conflict in Southern Iraq. Included in this assessment, Iran is training their soldiers to fight an guerrilla style war.
First let me say I'm not sure how we could manage to fight a war in Iran with our current deployment. I'm reasonably sure that the public would be a tougher sell then they were on Iraq, and Congressmen would feel a bigger risk in authorizing an invasion. That said, it seems the Bush administration is not one to bog itself down in reality. So who knows.
But until our armed forces learn how to deal with an insurgent uprising (perhaps early prevention would be a start), I would imagine any country we invade on whatever pretense would fall back on that strategy to try and overcome our superior firepower and technology. While I don't doubt we eventually will win out in these conflicts, the best strategy would be to avoid them all together. None only would this be easier on our troops, but on those of us at home who would wish them a safe return.