Did you know that Chinese people can count to ten on one hand? They have special hand signs for the numbers 6-10, and they are frequently used whenever numbers come up (for example, when giving prices in the market). Sometimes these hand signs help distinguish between 4 (si) and 10 (shi), which can sound alike.
Here is your mini-tutorial:
I also just came across a cool page that gives the meaning of gestures in the West and in China. There's some great Chinese translation on the page for those of you learning the language, and also interesting descriptions and pictures for the rest of us. Here it is.