Before you start handing out advice to others, get your facts straight. Cobham is completely right. The bureaucracy in China is clamping down hard on the 'F-Visa' brigade. If you've never "heard of anyone being kicked out of China" for a visa violation, I suggest you watch or read the news. There were at least three widely featured cases in Shanghai alone last year of raids, arrests and deportation of teachers without the legal right to work here. Perhaps even worse than this are the constant 'pickups' by the PSB in places like Henan. I have friends who teach at a university there. For some reason, the university is unable to supply them with a Z-visa and so they are working 'illegally' on F's. The local PSB are well aware of this fact and routinely 'arrest' them. They then spend the day at a police station while the cops negotiate a 'fine' with the university. OK, it's not deportation, but who wants to spend the day in a police station?

I'm sure there are cases where particular regional authorities turn a blind eye to visa shenanigans. This is somewhat true of Guangdong, where I work, but it is NOT true of everywhere in China, particularly the backwaters which are often militarily sensitive. The bottom line is that China, like all countries, has laws, and they are unequivocal. If you want to work here, get a Z-Visa. If your employer can't get you one, both he and you are breaking the law of the land and putting yourselves in what at the very least is a vulnerable position. It's that simple.