I can't tell you about Shanghai.
Beijing is huge with lots of Volkswagens believe it or not, made in China.

I found it dreary when I went.

For nightlife the best area is the Sanlitun entertainment area; everything from restaurants and pubs to discos and girly bars.
Lots of foreigners so you won't feel out of place.

Oh, yeah, and lots of Chinese food.

Unfortunately the Chinese have a bad habit: Spitting.