Cheng Jianping was arrested October 27, 2010, after retweeting her boyfriend’s tweet. Given that Twitter is banned, as the article’s author points out, it demonstrates how closely China monitors its citizens.
more importantly, they closely monitor whoever is considered as an activist. Cheng was probably on their lists for a while, but not her boyfriend (who still has not been arrested – let’s hope he won’t by the way). So people are blacklisted and then tracked down wherever possible on the internet.