Andrew Sullivan is the one-man, citizen journalism aggregator of the protests in Iran today. His collection of Tweets and YouTube videos convey the impression of a large-scale uprising that the government is trying to control with riot police, chemical weapons, and propaganda. It certainly appears that the uprising is gathering steam and that the government is out-matched. Given that the Supreme Leader relies on his moral authority to govern, and that authority is now shot full of holes, it seems unlikely that he can hang on to power.
Twitter and YouTube are certainly playing a role in getting the news out of the blackout the Iranian government has sought to impose.