An article from Sunday's NY Times talks about how cities are becoming places for the rich and the poor but not the middle class.
Unfortunately, the article fails to address the two main reasons for why the middle class have left the cities:
(1) Zoning laws prevent new housing from being constructed, raising the cost of housing so that the middle class can't afford it. But ghetto neighborhoods and public housing remain resistant to increases in housing costs, so the poor remain even though the middle class are forced out.
(2) School systems full of racial minorities and poor children scare away middle class families to suburbs with more homogenous public schools. Only the rich, who can afford private schools, or the poor who don't care because it's their children who are ruining the schools, remain in the city.