Joe Klein sees the strange episode as I do, a sign of dueling among Iranian government factions, and possibly indicating a conciliatory tilt towards the US:
Today, the American journalist Roxana Saberi was released from prison, which is excellent news but doesn't diminish the outrageousness of her incarceration in the first place. This much seems clear: Some faction in the Iranian government wanted her in jail on trumped up charges--a message of intransigence. And some other Iranian faction wanted her released--a message, potentially, that Iran is ready to begin negotiations with the U.S.
--Michael Crowley