I have to say my skepticism about this new medium has now disappeared. Without it, one wonders if all this could have happened. A reader notes a few facts:
Ahmadinejad's and Khamenei's websites were taken down yesterday - I saw the latter go down within a couple of minutes because of a DDOS attack organised via Twitter. @StopAhmadi is a good source for tweets on this. The other important use of Twitter has been distribution of proxy addresses via Twitter. This would be how most video and pictures of today's rally have gotten out.
Technology has not just made the world more dangerous; it has also enabled freedom to keep one small step in front of tyranny and lies. One thing you can do is use Twitter to fight the regime yourself. Help bring these fascist bastards down at the end of your modem.