The blog Tea Leaf Nation has written about a fascinating Harvard study that shows what posts get censored in Chinese cyberspace and why. The blog post (and the study itself) are worth reading in full, but, briefly, the study postulates that while censorship attempts to obfuscate it also "exposes an extraordinarily rich source of information about the Chinese governmen’s interests, intentions, and goals" (italics in the original), and that the government doesn’t necessarily censor posts with "negative, even vitriolic criticism of the state, its leaders, and its policies," but rather focuses on "comments that represent, reinforce, or spur social mobilization, regardless of content."
The second point especially seems to be a more nuanced understanding of Chinese censorship: someone blowing off steam is fine, even if it’s "unambiguously against the state and its leaders," as long as it doesn’t encourage destabilizing action.
As an example, the researches cite the posts on the Chinese internet after the Fukushima nuclear meltdown in March 2011, where some Chinese who believed (incorrectly) that salt would help protect them from radiation poisoning wanted to rush to buy salt. The study found that posts about the salt rush were heavily censored because they are "highly localized collective expressions that threaten to encourage group formation" even though they don’t directly involve criticism of the state.
Contrastingly, the researchers cite a post which they describe as an example of a criticism that the censorship apparatus left untouched: "this is a city government that treats life with contempt, this is government officials run amuck," the post reads, "a place where officials all have mistresses, a city government that is shameless with greed." A good reaffirmation that there is a space for civil discourse (or rambling screeds) on the Chinese internet.