From the WSJ. Some summary quotes:
"While the West approaches diplomacy with sincerity, the Islamic Republic mocks diplomatic convention to shield subversion."
"Tehran may still conduct diplomacy to fish for incentive and reward but, at its core, Iranian diplomacy is insincere. The Iranian leadership will say anything and do anything to buy the time necessary to acquire nuclear capability. That Foggy Bottom still advises against any strategy that might undercut the possibility of some illusionary breakthrough signals triumph not of realism but of negligence. Diplomacy cannot succeed if one side is playing for real and the other only for time."
Since this was written before Ahmadinejad's speech yesterday, here is a link to the transcript of his speech.