This Observer article on the Iran situation (via quoting) makes two excellent points that I stressed in my critique of Bush's invasion of Iraq:
(1) The whole WMD fiasco completely discredited US intelligence. So now Iran would be much bolder in developing weapons since world opinion wouldn't trust Bush et al.'s warnings about a bomb.
(2) Looking at what happened to North Korea compared to Iraq, what would the rational (though admittedly evil) ruler of a small country do: DEVELOP NUCLEAR WEAPONS AS QUICKLY AS POSSIBLE.