Joshua Kucera contends the protests over the current election results in Iran might be overblown b/c the tweeters there are creating an impression that there are more Reformers than actually exist. The implication of his post is Twitter is harmful because people are out on the streets protesting and getting beat up on the basis of an illusion that others will arrive to back them up.
Thomas L. Friedman has argued that it is hard to know how many protestors are out there because of the chiling effect of bang bang versus tweet tweet. He also points out that if the election was valid, then why does Ahmadinejad not allow the Europeans to confirm the results? It would only reinforce his position.
However, I've read elsewhere that it is important to remember the people who tweet, blog, and facebook tend to be college students who are only one slice of the Iranian Pie. They are not representative of the whole population.
In the end though, Friedman points out a benefit which might cancel the possible harm which Kucera warns us about. He argues that Facebook and Twitter offer a Virtual Mosque for the Reformers because they are places for refuge in much of the same way mosques offered havens for religious believers in the past. It is there, a place set apart from the state, in which grievances can be aired, minds can be persuaded, and strategies can be devised.