If you have been watching the news you probably noticed that Iran tested several missiles recently. On the news programs I have watched Iran is getting a lot of flack for this. In my opinion, the launching of the missiles was a smart thing for Iran to do. Israel had recently done a large-scale air force exercises which is what spurred Iran to do it's test. Iran's test was mostly a warning saying don't attack us we can attack you. For some reason, Israel is not getting as much flack as Iran is for it's tests.
A war with Iran would be extremely bad. All war is bad but comparing the war with Iraq to a possible war with Iran and it is much worse. Iran is far larger than Iraq, Iran has a much larger better armed and fanatical army than Iraq did, Iran has more resources, Iran has the capability to mess with the world economy in ways Iraq did not, and has missile capabilities Iraq did not. The war with Iraq has caused the death of hundreds of thousands of Iraqis and thousands of US soldiers. A war with Iran would have a far greater death tole.
I don't even think that Iran is building a nuclear weapon. Doing so might not be as bad an idea as a lot of people think though. Missiles and an army are not as much a deterrent for invasion as a nuclear weapon is. Iran is not making highly enriched uranium suitable for a weapon, only low-enriched uranium useable as nuclear power fuel according to IAEA (international atomic energy agency) report released on June 5th. US National Intelligence Estimate also has concluded that it probably gave up a nuclear weapons program in 2003. If Iran is doing what it is saying it is then it is obeying the Nuclear Non-Proliferation Treaty (NPT) that it signed which states a country has the right to enrich its own fuel to a level suitable for civil nuclear power.
Having said all that, I am of the opinion that Iran is not going about building their civil nuclear power plants in the best way. I think they should have agreed to the latest offer made by US, Russia, China, the UK, France and Germany that said Iran would get help with developing nuclear power stations and be guaranteed fuel for them. It would also be offered trade concessions, including the possible lifting of US sanctions preventing it from buying new civilian aircraft and parts. Though I do not know all the details so can not say with 100% certainty that would be the best choice, Israel after all seems to really want a preventive strike on Iran and has the nuclear weapon (also unlike Iran, Israel did not sign the NPT).
Personally I do not see Iran as being a major threat, no where near as much of a threat as say North Korea which already has the ability to make nuclear weapons and has missiles capable of hitting Japan. The Japanese defense budget for anti-missile technology has increased 10 times since North Korea has developed the nuke and they have been buying up a lot of anti-missile technology from the USA. They have also begun spending on militarizing outer space for defense purposes. There was even talk within Japan in 2004 about using preemptive strikes on North Korea (the nuclear option was even brought up), though this was shot down because it would anger China. If North Korea were to bomb Japan the fallout would be far worse than a war with Iran, particularly if they used a nuclear warhead. Japan would stop it's no nuclear weapon policy and start building them like crazy as well as other countries in Asia. Japan has the technology, raw materials (massive amounts of plutonium from its 50 nuclear reactors), and the capital to produce nuclear weapons within a year. This would lead to all kinds of tension (Japan and China historically do not get along what with the types of things Japan did to China during WW2 this makes sense) Japan would attack North Korea, but unlikely that it would be an occupation, Japan doesn't have the manpower for that, it does have the ability to wipe out most of the life in North Korea and other countries would be drawn in.