Reactions to the NIE on the right seem to be of two broad flavors. On the one hand, Captain Ed argues that George W. Bush solved the Iran problem in 2003 by invading Iraq; Iran was thus deterred from further pursuing its nuclear program. This is rather an odd argument, given that a) over the past four years conservatives have bitterly argued that Iran is too insane to be deterred from anything, and b) that conservatives still argue that Iran is fighting a proxy war against the U.S. in Iraq, meaning that the deterrent effect of the invasion doesn't seem to have had a terribly deep effect on Iranian foreign policy. On the other hand, Cliff May has a relatively simple explanation; the intelligence community hates George W. Bush, war, America, etc. and has no compunctions about lying to achieve its goals. The latter explanation at least has the virtue of internal consistency.
I think it's also fair to say that Michael Oren and Yossi Klein Halevi's fantasist article on Israeli perceptions of the Iranian nuclear threat hasn't aged well. Of course, if an Iranian nuclear weapon really could have produced the effects that Oren and Halevi imputed to it, including utter domination of the Middle East, the destruction of Israel without firing a shot, and total control of world oil prices, then it would have made sense for Iran to continue the program at high expense and risk. In the real world, of course, this was simply never the case; nuclear weapons are expensive for a lower-middle class nation to produce, and don't necessarily produce a positive security effect commensurate with their economic and political costs.
To be charitable to Captain Ed and the rest, I think it's possible that U.S. activity in Iraq may have had some effect on the Iranian decision. First, the destruction of Hussein's regime removed the greatest threat to Iranian security, and ensured that Iran would have a greater influence over Gulf affairs whether or not it produced a nuclear weapon. Second, it must have been apparent to the Iranians by the mid-summer of 2003 that, while the United States had successfully removed the Iraqi regime, it would not be able to attempt a similar operation (much less the far more difficult task of subduing Iran) in the near, medium, or long term. In other words, the invasion of Iraq served to multiply the costs of military action against Iran, a development that the Iranians no doubt understood and took seriously.
-- Robert Farley