The new sanctions, which the UN imposed June 9th, allowed UN nations to inspect ships headed for Iranian ports, to check for contraband, and seize it if found. The Iranians have threatened military retaliation against any inspection attempts. Iran is in a very weak position militarily, although official Iranian announcements would have you think otherwise. But decades of sanctions, and plenty of evidence (from cell phone cameras, satellite photos and testimony of Iranian military personnel who left the country), show that Iran has little real military capability (except against its own citizens). If Iran tried to close the Straits, there would be a fight between the modern forces of the West and the Arab Gulf states, and Iran. While the Iranians can be troublesome (especially with naval mines and land-based anti-ship missiles) at sea, Western navies have trained and equipped themselves to deal with whatever the Iranians can do. While there could be come temporary surprises, long term the Iranians are toast, and under blockade, plus their armed forces would be continually hammered by superior aircraft and missiles. For over two decades, the Iranians have diligently avioded putting their armed forces to the test of combat. This is the reason. There is no there there. But the world (Gulf Arabs who produce the oil and the rest of the world that buys it) does not want to even risk a temporary closure of the Hormuz straits, and the Iranians take advantage of that to make threats they can't back up.
The most recent public opinion survey in Arab countries shows that 57 percent now believe that Iran getting nuclear weapons would be good for the Middle East. This says more about the desperation of people in Arab countries, which continue to be run by corrupt despots. In addition to being corrupt, these governments encourage, or order, their mass media to blame the West, especially the United States, for all the local problems. Then, when opinion surveys come along, Iran with nukes makes people think that the West could finally be forced to make all the local bad stuff go away. It's won't, but that's how public opinion works in the Middle East. Arabs still consider Iran the enemy. But Arabs have so many enemies, including their own governments, that sometimes an enemy, for a while at least, seems like a solution. Iran has generally ignored all pleas and pressure to halt their nuclear weapons program (which they publicly insist does not exist, but privately boast of).
The new sanctions, which further restrict Iranian access to the world banking system, has helped the Iranian economy temporarily. That's because many Iranian investors, particularly wealthy (via corruption) clerics and government officials are getting money out of offshore accounts (where it might be blocked or seized) and back to Iran. There it is available for investment. But those who got rich through corruption still prefer to keep some of their wealth outside the country, just in case there's another revolution and they have to flee. Chinese banks are hustling after this business.
The new round of sanctions have forced Iran to scramble, and find new sources for banking and insurance services, not to mention a lot of goods that were not hard to get before. For example, the sanctions are hurting when it comes to gasoline (petrol), most of which has to be imported. Countries will break the blockade, for a fee. Iran can buy gasoline, which normally costs $700 a ton, for 20-30 percent more on a growing black market willing to sell to Iran despite the sanctions. But many nations are now halting shipment of major items, because of the new sanctions. Russia, for example, has held up delivery of five Tu-204 airliners (worth about $40 million each). These aircraft contain U.S. components, like the engines (which are built in Russia under license.) As a result, Iran is more and more dependent on China, which has invested over $40 billion in Iranian oil and gas projects. China doesn't mind ignoring the sanctions, because China believes they are too big (economically) and powerful (militarily and financially) for anyone to mess with.
Alarmed at the sharp slowdown in the population growth rate over the last decade, the government is now offering cash bonuses for new babies. The government wants to double the current population, to 150 million, so that Iran will be a stronger military power. In the last decade, the birth rate declined from 3.2 to less than one percent. The government explained this as a successful government population control program, but young couples were not having kids because of poor economic conditions and political repression. Meanwhile, the government continues that repression, shutting down any media deemed potentially dangerous and sending more dissidents and reformers to prison.
August 4, 2010: Iran says it has obtained four S-300 missile systems (apparently Belarus, which is currently feuding with the Russians, and China, which does whatever it wants). Russia has refused to deliver the S-300 anti-aircraft missile systems (bought three years ago by Iran). Russia has been pressured (and given counteroffers) from the U.S. and Israel to not deliver the missile systems, which would complicate any air attacks on Iranian nuclear weapons facilities. The S-300 sales is worth over a billion dollars, and the ailing Russian defense industry really needs the money. But the Russian government is increasingly upset at Iranian support for all sorts of Islamic radicals (including some operating inside of Russia.) The Iranians will not cooperate, and curb support for Islamic radicals that threaten Russia. A less discussed reason for not delivering the S-300s is Israeli claims that they have technology that can neutralize the S-300 radar and missile guidance electronics. That may or may not be true, but the Russians are not eager to see yet another of their weapons defeated by Israeli countermeasures. Meanwhile, China can keep the Iranian S-300s operational by providing technical support. China is the largest user of S-300s outside of Russia.
August 3, 2010: President Mahmoud Ahmadinejad had a hand grenade thrown at him as he was being driven to a rally south of the capital. Within hours, the official news reports were changed to indicate that someone had set off fireworks near the presidential motorcade, and there had been no assassination attempt. Nothing to see here, move along.
August 1, 2010: U.S. military officials admitted that there were plans for an American attack on Iran, to destroy nuclear weapons programs there. These plans are constantly updated, because the U.S. believes that it might not want to deal with a nuclear armed Iran.
July 29, 2010: U.S. military commanders revealed their concerns about Iranian terrorist operations in Latin America. Not just Iran, but also Iran-backed groups like Hamas and Hezbollah. Iranian ally Venezuela has provided a safe base for Iranian operations in the region.
July 26, 2010: The EU (European Union) adopted some even stronger sanctions against Iran than what the UN imposed in June. The U.S. has the strongest sanctions against Iran, and is becoming increasingly effective at making them work.