Freakonomics: How should we be thinking about urbanization?

The Freakonomics blog over at the New York Times recently put together a panel of experts to discuss the world's rapid urbanization.

Contributors James Howard Kunstler, Edward Glaeser, Robert Bruegmann, Dolores Hayden and Alan Berube were asked to answer the following:

"This year marked the first time in human history that more people lived in cities than in rural areas. What problems and opportunities does this present? What effects has it had on our local and global culture? Economy? Health?"

Predictions ranged from positive to very, very bleak.