In an analysis done of census data pre-housing boom (1990s), The Brookings Institute in their recent report Where Workers Go, Do Jobs Follow? found that:
- Roughly 65 percent of all residents and nearly 60 percent of all jobs are now located in the suburbs, with over a third of each in the higher-income suburbs.
- Population grew strongly during the 1990s in the lower-income suburbs, while job growth was particularly strong in the higher-income suburbs
And then comes the 2000s
The New Urbanism  movement, bolstered by the housing boom’s creation of new luxury housing stock and redevelopment of underutilized commercial districts, has seemingly reversed the long term migration to the suburbs. The decline in serious crime levels in urban markets have also played a major role in boosting demand (and may in turn further influenced the decline)
Will the current economic downturn undo urban housing trends in many US cities?
Based on the St. Lousi Fed research paper City Business Cycles and Crime  by Thomas A. Garrett and Lesli S. Ott , perhaps not:
We find weak evidence across U.S. cities that changes in economic conditions significantly influence short-run changes in crime. This suggests that short- run changes in economic conditions do not induce individuals to commit crimes…we do find that short-run changes in economic conditions influence property [versus violent] crimes in a greater number of cities.
I have always seen crime levels and other quality of life issues as long term trends, like steering a super tanker (admittedly, a tired analogy).
And while we are on the subject of research papers…