I got this from a friend of mine today and wanted to pass it along.
"Twitter is increasingly becoming Iranian protesters' lifeline to the outside world, as international news organizations are banned from covering the demonstrations."
If anyone is on twitter, set your location to Tehran and your time zone to GMT +3.30. Security forces are hunting for bloggers using location/timezone searches. The more people at this location, the more of a logjam it creates for forces trying to shut Iranians' access to the internet down. Cut & paste & pass it.
So get out there and join the revolution.