I've always wondered how China actually implements their Internet censorship, and how effective it is. I could have probably found out by doing some online research, but as with many things it just never happened.
Since I'm now using it every day here in Shanghai, I think I have a pretty clear picture on what is going on. Apparently all they do is some URL based HTTP filtering, and black-holing those requests. I'm not sure whether they actually filter all traffic to the black-holed IP address (which could shadow thousands of other virtual hosts on the same address), or actually only filter individual requests.
So apparently they're just blocking the technically unsophisticated regular user. Anyone with some basic network knowledge could easily work around those restriction - though it probably would be highly illegal.
So basically all the websites I want to access - including those that definitely contain content that the Chinese government would dislike. The only thing that is lacking from the web for me is wikipedia. But well, if you google for the term that you're searching in wikipedia, then Google will happily give you the Google cache of that page ;)
But there's definitely no filtering on ports such as SSH or IMAPS. I can transparently access my IMAPS-secured mail server, I can ssh to my machines in Germany, everything working quite fine. Obviously any kind of tunnelling would give me access to the free world.
So all in all, (luckily!) not very effective, from my point of view.
Now I hope that the Chinese authorities don't see that posting before I leave the country, interpreting it as a 'censorship protection circumvention technology', or actually put my blog into their filters ;) This page is uploaded via HTTPS, so at least they won't see this message _leave_ the country.