Thanks, that is awesome info. In 12 months from now I will possibly be in the situation you described, doing a visa run to HK, so this is great stuff.
I am in NZ at the moment, and the school in China I just have accepted a contract with said it will take about 2 weeks to get the documents processed in China, 3-5 days to express mail them to NZ, then it takes about 3-5 days to get the entry visa and temporary Z work visa from the local Embassy here.
So just to be clear, once in China it is much easier to renew a contract and Z-Visa if you stick with your present employer? Is this done without having to do the Visa run?