China has an estimated 30,000 to 40,000 e-police watching over its 100,000,000 users. According to Newsweek, the Chinese government is more interested in preventing demonstrations than controlling information itself.

Newsweek : Big Brother Is Talking

Quote Originally Posted by Newsweek
Beijing's Web commissars have made a quantum leap in their efforts to tame the Internet. Much has been written already about Chinese censors' ability to monitor Net postings; to block or delete undesirable content, and to detain Netizens deemed to be troublemakers. The larger story is the degree to which China's e-police now proactively influence Web content in ways beneficial to the regime—and pre-empt people from organizing politically. The aim is not simply to stifle dissent or to control the free flow of information, but increasingly to shape public opinion in cyberspace. In fact, Chinese propagandists worry less about the Web as an information source than as a tool for mobilizing mass movements. "Most foreign analysts get it wrong," says Anne Stevenson-Yang, a Beijing-based Internet entrepreneur. "Political concern about the Internet is totally about social organization, not about information. It's how you act on the information you have."
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That emphasis suggests authorities aim to avoid any repeat of last spring's unrest. Then, spontaneous bulletin-board postings and SMS text messages inspired thousands of youth to participate in anti-Japanese protests, catching riot police off-guard.
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According to the OpenNet Initiative, a project involving researchers from Toronto, Harvard and Cambridge universities, China has "the most extensive and effective legal and technological systems for Internet censorship and surveillance in the world."

Much of that effort uses sophisticated "filtering." Chinese routers—most of them made by Cisco Systems—connect local area networks to ISPs and can be configured to block up to 750,000 Web sites. Keyword-filtering software installed on all Web-site hosting services automatically bar postings on Chinese online forums if the titles include certain buzzwords.
I am not sure how efficient automated filtering really is. Blocking websites by keywords would inevitably block much more than just the unwanted content.