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There are new rumors of what drove the early release of the hostages coming diverse sources such as Debka and Strategypage.com. Debka has always been suspect, but Strategypage.com has been more reliable and through in their analysis. They indicate that Ahmadinejad and his radical fringe lost to a more conservative Khamenei and his plans. RUMINT has it that Ahmadinejad was trying to use this to try to provoke a confrontation with the US by striking a weaker coalition partner.
Note the trend; Iranian rhetoric proceeded to an eventual crescendo threatening to try the hostages for treason. Suddenly, there is a change in plan and they are released on the prophets birthday with no apparent strings attached. This switch was due to Khamenei stepping in and overruling Ahmadinejad. Debka also notes that the PR effects suffered greatly this time around and it did more to hurt Tehrans goals than help. Thus now Tehran is trying to milk the generosity that they have shown.
The potential for something more serious to occur in the gulf remains. If Strategypage.com is correct, this is the second set back for Ahmadinejad. As a radical believer, Ahmadinejad believes he is on a mission from god, and failure is not an option. Thus his next attempt might be more dangerous and actually trigger a shooting war with the US.