I am looking for reliable stats on the effectiveness of internet censorship in developing countries.

You should try Ben Edelman's empirical stuff on Internet filtering in China: http://cyber.law.harvard.edu/filtering/china/ I think this is the most reliable method going, though I have heard a counter-argument that the poor overall quality of Internet infrastructure in China gives Edelman false positives. (That is, the sites are unreachable, but not blocked.) Christian