@Chung - yes, it's dirty, but pretty typical for air quality for large asian cities. Not much worse than Saigon, for example.

I've never been there, but I heard that the air in Beijing is really dirty.

I recommend the peking duck and roast lamb if you are a meat eater. The forbidden city and the great wall are awesome.

Some things to be aware of: crowded places can be pretty scary, as anything goes in a crowd in China. Smoking is allowed just about everywhere, especially in restaurants.