There is almost nothing you can't buy in China, except freedom.
One factor of the freedom is freedom to acquire information from the Internet. Depends on which gateway your ISP uses, you may experience different level of quarantine from the rest of the world. Some luxury hotels are allowed generous access to news sites such as CNN or NBC; while most residential customers are blocked to almost everything even remotely related to 'news'. Youtube, for example, has been blocked for months. Surprisingly, the most isolated browsers are found within ivy towers. Universities in China are connected by a so called 'Education Net'. Faculty and students alike will need to pay extra to pass a gateway of the Education Net to gain access to the Internet. However, even so, a much broader list of blocked sites are checked at the gateway of the Education Net. Many of the sites blocked by the Education Net are legitimate and dedicated for education purpose. For example, Conference Hub, a journal review site was blocked by the Education site, for no obvious reason. Also, HPC Wire, a long time news service in High Performance Computing, is also blocked by the Education Net, but not by regular residential services. It could either be the result of tighter control on college students, or a reflection of self-censor conducted by education officials.
Fortunately it is not difficult to make a break, and most Chinese students know how to do this. For foreign travelers, the key is to make preparation 'before' you enter China.
First of all, there are (at least) two levels of control over the Internet: Blocking (by a list) and Active Filtering (on dynamic contents). Websites such as YouTube, WordPress, SNS, Yahoo (Taiwan), Plurk, Blogger (including this blog) are blocked by a frequently updated list. From time to time, sites such as Google, wikipedia, New York Times are also placed on the list when necessary. Last week, the CCTV aired an interview with a college student who claimed to be a victim of Google. The student told the reporter a story of his roommate searched pornography stories on Google and masterbate in the dorm. Subsequently, Google China was suspended for a few days. Google agreed to cut regular 'Google' service to Chinese residents, and only provide an 'improved' service to China with dedicated servers located inside Chinese boarder (so that they could be closely monitored by the police).
In addition, any pages containing sensitive words are denied by the Great Fire Wall (part of the Golden Shield project). The Golden Shield works in both ways across gateways between mainland China and the rest of the world. When a user trying to access pages containing sensitive words across the boarder, the connection will be reset for a very short time with minimal impact of other functions. The technique is developped jointly Cisco on contract with the Chinese authorities.
It is not that Chinese Internet users had not put up a fight. April 2007, Shanghai resident Mr. Du Dongjin sued the China Telecom on terms of contraction violation for blocking realcix.com (why?). He lost in two courts. June 2008, Beijing resident Mr. Liu Xiaoyuan sued Suho for blocking his personal blog, the court refused to register the case.
For the rest of us, the most easy and straight forward way of breaking the blockage is by using tor, an application which can divert your traffic through a network of volunteer nodes (proxy). However, the Golden Shield monitors and blocks any reference to 'tor'. The official Tor Project site is blocked. Therefor, you are almost desperate once you get in China unprepared. So the key is to be prepared before you go.
For Windows user, you can download a 'tor' bundled with a browser on your USB drive. It's a portable 'green' application, which does not need to be installed to start.
For UNIX/Linux user, it's a little tricky. You need to install the required service components: tor/privoxy/squid. You also need to edit a few lines in the configuration file of privoxy. For most modern distrubutions, you can install them pre-compiled with system installation tools. A step-by-step instruction can be found here. Fortunately, this page is not blocked, yet.
An 8th grade student in Beijing Zheng Jiehan 'doggie' made a PowerPoint presentation on the Internet censorship in China.