A bit of history and some warnings.
Huffington Post liveblog coverage
Semi-organized live firehose: http://iran.twazzup.com/ (selected twitter bloggers plus relevant keywords, updating live)
If anyone wants to wade through what I already shared today from Twitter, I have this morning's tweets archived already, thanks to wibbble, who tweaked the usual posting script to run twice today in case I overloaded it (and it was a good job he did, because it would have).
Right now activists are pleading with Twitter to postpone their maintenance, because people in range of the chaos are using it as part of their communications network, and Twitter going down would endanger their lives.
People following, my dears, please take time to see to your own needs as well. Tweeting and retweeting, you are a node passing packets, and the network heals itself if one node has to go down, so long as there's a network. This is the model the internet was built on. This is how it works.