I don't always agree with Paul Krugman, but in his Op-Ed today he makes an interesting point that often goes unmentioned when suburban lives and urban lives are debated. Despite positive changes in income and crime, many people will always associate urban and high-density living with poverty and danger.  Krugman's words:

"And there are, as always in America, the issues of race and class. Despite the gentrification that has taken place in some inner cities, and the plunge in national crime rates to levels not seen in decades, it will be hard to shake the longstanding American association of higher-density living with poverty and personal danger."

This, I believe, is a bias that we've created for ourselves. Now that an entire generation of children has been raised in the post-WWII suburbs, we have an entire generation of new parents who now believe the suburbs is the only place to raise their children safely.