Blocked again

Wikipedia.com is blocked in China as always. Blogger.com and Flickr.com are blocked in China now and then. The censorship system seems triggered by keywords. If your site has those words, your whole site is blocked. The mechanism seems too harsh for Web 2.0 sites, for example, the sites mentioned above. Those sites' contents usually are aggregated by million of internet users. One user posts some sensitive contents. The whole site is blocked even though tons of others are harmless to any party.