Lorenz curves actually haunt me in my sleep at times as an Economics major. They are most often used to determine the measure the inequality of a population based on the income of the population. They can be used to derive important figures to the study of economics such as the Gini coeffecient (seen below).
Found - http://450.aers.psu.edu/images/gini.gif
This blog is a map catalog in which I am displaying fifty different types of maps and a tid-bit of information that looks into the purpose of the map!