A May 2007 article from the Economist still seems like one of the better surveys of urban growth that I have read.
With that said, let me give a bit of a personal perspective and see if this resonates with anyone. Until I was 17 years old, I lived in a town of less than 5000 people in Northern Illinois. No one asked what school I went to, there was only one option. The only major fast food chain was Hardee's and Main Street was truly the main street. Over the years, I have seen the exodus of people my age and younger leave to head to Chicago, the nearest big city or to the four cornes of the earth. Why? First, two major factories shut down. The General Electric and Ethan Allen factories, which used to employ about a third of the town, each closed.