Google China has censored their search results to remove certain sites and listings that are deemed by the Chinese government. However, an advertiser has discovered a loophole in the censoring system that results in these censored sites showing up in google.cn search results via the Google AdWords sponsored listings program.
The blog Internet Censorship Explorer (ICE) ran an experiment using the site Human Rights Watch which does not appear in Google China search results. However, it was discovered that the URL filtering does not seem to apply to AdWords listings, as an AdWords ad with hrw.org as the display and destination URL of the ad showed up for keyword and site searches.
Although ICE recommends this as a way to circumvent the censorship of Google.cn, I would suspect that this loophole will be quickly closed for censored URLs as well as for specific keyword searches.