A few weekends ago I rode the train from Washington to New York City. Along the way, I noticed that many cities (mainly Philadelphia and Baltimore, but parts of New Jersey too), basically looked like war zones: abandoned, half torn down factories, row houses with trash in the street, and couches thrown down into the culvert near the tracks.
In some respects, I think that the cause of this is similar to what happened in Detroit and other rust belt cities during the 1960s, '70s, and '80s, the outsourcing of labor combined with the white flight created lots of urban decay and cities that were primarily industrial had to change. This also begs the question of "why did this not happen in Pittsburgh?", but that's a different topic.
One thing I also noticed was that as the industrial brownfield was being re-developed, housing projects were being built, not mixed use development, but housing projects. I'm beginning to wonder if it would be possible for the housing market to outgrow the job market if this development style continued, what would be some of the consequences of this happening if it were to occur? In my personal and un-professional opinion, I think that severe urban decay is best combated with mixed use development, as it provides housing and the commercial space serves as both a source of goods and services and a source of jobs. What say you? Granted, I have never been able to get my hands on any real literature surrounding this topic, so I don't know what is actually happening, I'm just discussing what I perceive to be happening.