They refer to China mainland and Hong Kong as "one country, 2 systems", which basically means that Hong kong's GDP is counted in China's GDP.. but that's all they have in common. For me (UK citizen), I can travel to HK for 6 months visa free, but my chinese girlfriend needs a visa to go there.. even though its part of 'her country'.
So for China mainland you'll need a temporary (3-6 months) visa for sure. But i think its very easy to get, a friend of mine from Serbia came to work 9 months with me and he had absolutely no problem. If you want to live there 'permanently' though, you need a work permit or need to marry a Chinese lady... both are not too difficult either though.
Internet censorship is a joke, I have a VPN I pay $11 for 6 months, and I surf the internet like I was in the USA. Without a VPN its a pain though, Facebook, twitter, youtube.. all blocked; but you have the chinese copy sites (weibo, renren, youku). just all in chinese, lol. But with VPN, its absolutely fine.
The only reason why I don't want to live here permanently is the pollution, which is pretty bad. Apart from that, its nice here, food is awesome, girls are awesome, nightlife (in the big cities) is awesome, business is super-awesome.. everything is so cheap. You should definitely consider it, at least try and find a company that recruits you for like 6 months, and get a feel for the place, some people never leave, others never really adapt...