Then take Sudan. Where the initially imposed sanctions aimed at government overturn. Suddenly China showed up in Sudan as a great investor in crude oil extraction and exploitation. Sudan is now selling all of its oil to China rather then to the West as it did before, and most of Sudan's oil industry is in the hands of the Chinese.
On the other hand, sanctions may just work their, err, "Chinese drop" effect by grounding the living standards in Iran and thus helping the case for more anti-government protests. At the end of the day, unemployment and starvation usually beat patriotic feelings down to mass revolt. It happened before in Iran, just not quite enough to reach a tipping point and cause an overthrow of Iran's leadership. "Sanctions on Iran right now are potentially quite effective because the Iranian government is stuck between a rock and a hard place, if they keep spending on their nuclear programme they'll have less money to placate the general population and face protests from greater numbers and with greater intensity."
Sanctions, together with subversion, are a better option than open war. To get out of this corner, Iran has to refactor crude extraction and export facilities, ports, etc. It shouldn't be a problem to increase their oil transportation infrastructure and boost oil production by installing more pumps -- only if Iran had the money and support of companies like BP, Exxon. Which is not the case.
On the European continent, this could turn out as more bad news. The Eurozone financial crisis contributed to skyrocket fuel prices at the pumps. This geopolitical decision is most likely to be played by politicians and traders in order to justify more price hiking.
The US imports no crude oil from Iran whatsoever. So playing the Iranian oil card in the American economy is just nonsense.
The EU nations import 8.5 million barrels a day. USA: 13.5. Japan: 5.5. China: 4.5. South Korea: 2.5. What if all of them will ban crude imports from Iran?
"Japan is already one of Iran's biggest customers. Not long ago, Iran asked Japan to pay in Yens (which of course in hindsight seems incredibly wise, as the yen has almost doubled in value since then), one of the first really big oil contracts to be denominated in a currency other than dollars. Should be an interesting diplomacy game to see if Washington is even able to convince Japan to restrict Iranian oil imports..."
2012 looks anything but boring.