Angus McDowall has a good article about this very issue:
Last night's dramatic footage demonstrates how extremists with a grudge against the West and a burning sense of ambition can force Iran into sudden confrontations that its smoothest-talking diplomats can have trouble defusing. The revolutionary guardsmen and their radical supporters behind this crisis only represent a single faction. But they have been able to take Iran's foreign policy hostage and provoke an international incident.
Taking advantage of the deep fractures in the Iranian state, the revolutionary guards have created a fait accompli, forcing the government to adopt a position from which it will be hard to back down. Driven by their experiences of the revolution and eight bloody years of war with Iraq, many guardsmen want to see Iran take a more aggressive stance against Britain and America. The confusion is caused by Iran's unusual political system, which combines democratic elements such as an elected president and parliament with the theocratic rule of a supreme leader. In practice, this means decisions are rarely made by a single person: they are disputed and fought over by a host of political factions and vested interests, including religious leaders, elected politicians, wealthy merchants -- and soldiers.
I also agree with parts of what The Moor Next Door says about Iran's capture of the 15 British sailors:
This move lacked tact and subtlety. This kind of bold behavior irritates enemies and solidifies their alliances. This sort of action simply validates American perceptions of Iranian behavior (which are often incorrect, and even dangerous, in their judgements, because they are usually hysterical and spasmodic), and serves to potentially transfer those across the Atlantic.
(Found via Global Voices)
Last night, we decided to start a pool (I know, it's crass...) for when the sailors will be released. My guess is 15 months (everyone thinks I am nuts. I hope they are right), Keivan and another friend think sometime next week after Sizdeh Bedar (the 13th day after the New Year and the last day of the New Year's holidays). No one else was brazen enough to hazard a guess.