Spartacus in Iran

Anonymity requires cover -- people who could plausibly be the anonymous person, but aren't. I've called this the "I'm Spartacus" effect, and real researchers have studied it more rigorously.

One of the most-repeated tweets regarding the Iran election is a plea for everyone to change their profile, time zone, etc. to say that they're located in Tehran, in order to provide cover for people who really are.

I wouldn't expect this to be completely effective. I'm sure there are ways for the authorities to track down the source of tweets before they make it to the Twitter servers, just as there are countermeasures to avoid detection at the source. However, once the tweets reach the server and are redistributed, it probably does make the job somewhat harder for the authorities. At least they have to read through more tweets to decide which ones are likely to be home-grown.

If nothing else it provides a way of showing solidarity, on a par with tinting one's icon green.