A thought-provoking article in the Atlantic Monthly. Some salient extracts:
For 60 years, Americans have pushed steadily into the suburbs, transforming the landscape and (until recently) leaving cities behind. But today the pendulum is swinging back toward urban living, and there are many reasons to believe this swing will continue. As it does, many low-density suburbs and McMansion subdivisions, including some that are lovely and affluent today, may become what inner cities became in the 1960s and ’70s—slums characterized by poverty, crime, and decay.
[...]
Demographic changes in the United States also are working against conventional suburban growth, and are likely to further weaken preferences for car-based suburban living. When the Baby Boomers were young, families with children made up more than half of all households; by 2000, they were only a third of households; and by 2025, they will be closer to a quarter. Young people are starting families later than earlier generations did, and having fewer children. The Boomers themselves are becoming empty-nesters, and many have voiced a preference for urban living. By 2025, the U.S. will contain about as many single-person households as families with children.
[...]
Despite this glum forecast for many swaths of suburbia, we should not lose sight of the bigger picture—the shift that’s under way toward walkable urban living is a healthy development. In the most literal sense, it may lead to better personal health and a slimmer population. The environment, of course, will also benefit: if New York City were its own state, it would be the most energy-efficient state in the union; most Manhattanites not only walk or take public transit to get around, they unintentionally share heat with their upstairs neighbors.
There's a lot more than what I've quoted above, though, so read the whole thing.