Its not what you think. We've been using them for a motivational thing for Nate. His behavior was becoming challenging so we decided it was time for a "new" reward system to help get him interested in being polite, helpful, etc.
So, the way it works is this: for every good behavior there is a set (or sometimes random) bean amount that he gets to put in his jar upon completion of said behavior. For every bad/poor behavior there is a bean amount that gets taken away from his jar. There are rewards posted on the fridge w/ bean $ amounts to be paid to get the reward. Every few days we get to count the beans in the jar and see what he has and decide if he wants to buy something or save for something. At first he was buying piddly things like dollar store toys that get lost or broken quickly. But slowly he is learning to save up for the big ticket item like a date to the movies, etc.
It is not a cure for normal childhood behavior but it has been helpful in minimizing the tantrums and disobedience and maximizing the helpfulness and cooperation. Certainly worth the small amount of time, effort and money to increase the peace in our house!
Here are some links about kids & chores:
Chores for Kids by Age
SuperNanny Reward Charts (we used these when potty training Nate)
Printable Reward Charts