There's a recently-published book called "The Five People You Meet in Heaven". So I thought I'd introduce you to "The Seven Ex-pats You Meet In China."
First, the most common type. I call him (or her) 'the gapper' (as in 'gap year'). He is just out of university, and not sure what he wants to do in life. He will probably head back home to get a Master's/Education/whatever degree. He spends the first three months excitedly 'getting into the culture', and the next 9 months at the closest ex-pat bar.
The missionary. Usually an evangelical Christian, she (or he) wants to 'win souls for Christ'. Of course, missionaries officially aren't allowed in China, so she is 'undercover', even though everyone knows she is a Christian, travelling with a Christian organization. I'd say their success rate is about 2:1. That is, for every 2 missionaries who go to China, they convert on average 1 person.
The escapee. He (or she) is running away from a bad marriage, bad debts or other trouble back home. This is more of a 19th Century phenomenon, though, since divorce is so easy to obtain now, and you can't hide from Visa or the banks, even in China.
The diplomat/soldier. Also rare in China, although common in South Korea and other places with large U.S. military bases. He (usually it's a man) is serving his country abroad, often with his family. His children attend an international school in Beijing or Shanghai. I guess you could include the wives of diplomats/soldiers in this category.
The retiree/widow/divorcee. This type of ex-pat is far more common than you'd expect. She (usually it's a woman) has just retired or lost her husband, and therefore gained her freedom. She goes to China for much the same reason that the 'gapper' does. She often makes close Chinese friends (adults). She may have intended to go for just one year, but ends up staying 3 years, or longer.
The emigrant. There is really only one way to emigrate to China- and that is to marry a Chinese citizen. Although 'emigrant' may be a misnomer, as emigrants to China almost always return home eventually. But still, he or she is there for the long haul, buying an apartment, maybe a car (if he is exceptionally brave) and raising kids in China.
And, finally, the true ex-pat, who may have gone to Asia as any one of the above, but finds himself unable to truly assimilate, like the emigrant, or feel at home back in his native country. What can he do? He is stuck in the sandtrap of ex-pat bars, PC bar hangouts, and annual trips to Thailand.
Which am I? Well, if you haven't guessed, I started as a gapper, and I'm now becoming either an emigrant or a true ex-pat. Only time will tell.