Pollution
The pollution in Beijing isn't much worse then what you see in London but you'll only see Beijing on your own time. The company has offices in Beijing but there are no flight operations there of any sort. You'll spend your first 4 or 5 moths in Shijiazhuang and the pollution here is unreal. Some of the worst in China and China has the worst in the world. You'll develop the habit of hacking and spitting here on a regular basis (this is normal and you'll see everyone doing it, even old women--on the train, busses, even occasionally in hotel lobbies).
With a lot of luck you pass the tests on the first try and then you only have to wait 4 or 5 months for "standardization." When, or rather if, that ever happens you have a chance of being shipped somewhere else, most likely Batou. As Pat said the Batou base is supposedly better but I've only been there once so I can't speak much to it. There is one other base, Handan, which is opening next month (it actually looks like it might open in April but to put things in perspective, it has been "openning next month" since I got here in November and a lot of the others guys say it's been "next month" for a year and a half so take that for what it's worth).
The website is far, far out of date and the way communication works here I'd be leery of something else. They are drawing up a new contracts but it is doubtful they will send you the new one. Before I came they sent me the contract ahead of time for review but you will want to make sure they send you the new one, which is doubtlessly less in your favor. When you get here they won't reimburse your trip expenses until after you sign it so you'll want to minimize surprises.
As for the other benifits they will sell you on, namely "banking" days and bonuses, none of that exists anymore and they will change or take away anything they please with a few keystokes of an email. There is absolutely no protection for you anywhere in China. You're a foriegner, you don't speak Chinese and even if you did you would still lack the money and connections to seek any kind of legal protection. Anything that that happens here will be judged as your fault, automatically.
As far as China being the new aviation boom, don't hold your breath. They have to change a lot first and the one thing the Chinese loath above all else is change. Everything here is appearance and as long as it looks like modernization their goal has been met. Progress is a bit more elusive.
Positives: Good group of people to hang around with, learning a new culture, some travel oppertunities in the region, free living and easy money if you keep your head down.
As for the negatives, you'll have no difficulties finding those on those other threads.
Good luck,
Derek