The TOR website is blocked in mainland China, as is TOR itself, but it works via obfsproxy, all it requires is someone to send you the executable/source. Most people who bypass the great firewall use VPNs, however.
I once spoke with a student from China who told me bypassing the Great Firewall with a VPN is quite common. Not practiced by anything close to a majority of the population, but common enough that it would probably be used by e.g., that guy you know who couldn't tell Ruby from Python, and has never touched Linux, but is quite capable of figuring out how to fix his Windows box when it breaks.
I don't know the answer to this and of course the following was easily dismissed with a tinfoil hat comment, but when China decided recently to unban porn there were people suggesting it was to make bypassing the great firewall less 'necessary' for the average user.
