Some research on this topic:
Empirical Analysis of Internet Filtering in China (2003)
For some 1,043 of sites tested, we confirmed that DNS servers in China report a web server other than the official web sever actually designated via each site's authoritative name servers. We call this phenomenon "DNS redirection," though others sometimes refer to the situation as "DNS hijacking." Consistent with prior reporting by Dynamic Internet Technology, our data show that such sites were consistently unreachable in their entirety.
Filtering on the basis of keywords in URL. Beginning in September 2002, our data reflect that when a subscriber to a Chinese ISP submitted a URL request that itself contains certain words or phrases -- this typically happens for search engine searches, like http://www.google.com/search?q=jiang+zemin -- no response would be received.
Filtering on the basis of keywords or phrases in HTML response. Beginning in September 2002, the authors observed that certain keywords in HTML response pages seemed to be blocked by Chinese network infrastructure. In particular, even when a page came from a server not otherwise filtered, and even when the page featured a URL without controversial search terms, it might nonetheless be inaccessible if the page itself contained particular controversial terms. Such pages were often truncated, i.e. interrupted midway through their display.
Other Effects of Chinese Filtering: Routing. The authors have observed that some American ISPs route packets through China towards destinations beyond China (in particular, to Hong Kong). When the desired web servers are blocked from China, such a routing typically yields to filtering by network equipment in China of an American user's request. In response to this problem, affected American ISPs can address the situation by manually altering the routes used to reach hosts in Hong Kong and elsewhere. However, affected ISPs are often unaware of the situation, and an effective response requires delay and/or causes additional expense as an affected ISP finds the necessary partner ISPs and establishes peering relationships with them.
From the technical appendix: http://cyber.law.harvard.edu/filtering/china/appendix-tech.html
The Velocity of Censorship: High-Fidelity Detection of Microblog Post
Weibo and other popular Chinese microblogging sites are
well known for exercising internal censorship, to comply
with Chinese government requirements. This research
seeks to quantify the mechanisms of this censorship:
how fast and how comprehensively posts are deleted.
Our analysis considered 2.38 million posts gathered over
roughly two months in 2012, with our attention focused
on repeatedly visiting “sensitive” users.
We found that deletions happen most heavily in the
ﬁrst hour after a post has been submitted. Focusing
on original posts, not reposts/retweets, we observed that
nearly 30% of the total deletion events occur within 5–
30 minutes. Nearly 90% of the deletions happen within
the ﬁrst 24 hours.
ConceptDoppler is a weather tracker for Internet censorship. Using ConceptDoppler we can track the list of keywords that a government uses to censor Internet traffic. For GFC keyword filtering, we can also locate the routers performing filtering and deduce the architecture of this censorship mechanism.
We use Latent Semantic Analysis to prioritize the words we check. Just as an understanding of the mixing of gases led to effective weather tracking, understanding the relationship between sensitive concepts and blocked keywords will lead to more effective tracking of Internet censorship. More details are available in the paper.
Website with list of blocked keywords: http://www.conceptdoppler.org/
The third paper is a bit dated, but Jedidiah R. Crandall is now a professor and still working on combatting censorship; the second paper is from his department. Definitely worth checking out.