It seems (at least, according to the article below) that the Chinese government has learned from the Iranian demonstrations, in which (as people probably already know) Twitter helped people organize demonstrations even when all cell phone networks had been shut down.
http://www.examiner.com/x-15615-Asia-Headlines-Examiner~y2009m7d8-Facebook-Twitter-inaccessibility-makes-China-expats-feel-disconnectedor:
http://tinyurl.com/ksj8mxexcerpts:
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BEIJING The Chinese government's decision to disrupt service to a number of popular websites, including Facebook and Twitter, is making foreign residents in the Middle Kingdom feel cut off from the outside world. On blogs and news sites, foreigners living in China raged about not being able to communicate with business associates and loved ones overseas.
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and
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The Chinese government began blocking access to certain websites this week after violence erupted in Xinjiang, located in western China. The Chinese government confirmed that it was disrupting Internet access because it believed protesters were communicating via social networking sites. The government has not said when it will restore access, but in the past it has usually done so in a few days.
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Karen
http://karen.stanley.people.cpcc.eduCharlotte, North Carolina, USA