I think - for which it is my humble and unqualified opinion - that a definition of "expat" is not that easy and it might be a different idea for different people and personalities. What's the difference between an expat and an immigrant? I would assume it is the intention to go to another country, for that an immigrant has already decided to spend the rest of his/her days abroad. So the expat is more like a guestworker at the beginning, with the potential to become an immigrant later on. And one decisive factor to become an immigrant could be the level of happiness as an expat.
So, am I happy as an expat? - Well, I'm for sure a happy expat!
And how do I know that? - Because I am rewarded every time I go home and tell those crazy ol' Chinahand stories. And that's great, since it seems there's nothing happening back home at all. No crazy cabbies, no strangers taking photos of you and their kids and then inviting you to a wedding party, no totally-out-of-the-way "treatment" at the local hospital for a runny nose, and surely none of the things Simon described.
So, still an expat or already an immigrant?
I'm not sure, yet, at least in my case. But there are some indicators that I could make the transition.
People like me, with a lack in self-confidence, can - from time to time - get annoyed by the not ending affirmation to be different from the Chinese, by the Chinese, pointing to me calling me "Laowai". So, every time I go back to Germany I just enjoy not being called "laowai" by strangers.
On the other hand, I pretty much appreciate while buying groceries or paying my parking ticket in China being constantly praised for uttering some Chinese-like sounds, praises in form of "ni zhe ge xiao huozi shuo de Zhongwen bi women Zhongguoren hai hao, hahahaha".
But then, back at (what was formerly known as) home, no one ever, except family and friends, praised the quite good German of my wife, not the cashier at the supermarket nor the lady at City Hall. If they don't praise my wife's German, you are welcome to call my laowai 'till I die! Deal!