As Richard B. Freeman and William M. Rodgers III document, the past four years has been the weakest recovery from a US recession in the past forty years -- employment creation in the 2001-2004 period has fallen short of job growth in the recovery phase of all of the last six US recessions -- by a substantial margin. Freeman and Rodgers rightly reject the argument that rapid productivity growth should take the blame for slow job creation, emphasizing that productivity improvements increase the noninflationary growth rate of potential GDP. A final possible explanation is offered by accelerating structural change. The crucial characteristic distinguishing unemployment due to structural change from "cyclical" or "demand deficient" unemployment is the fact that "structural unemployment" occurs when workers are unable to fill available jobs because they lack the required skills or do not live where jobs are available. This implies that the number of vacancies is an upper bound to the extent of structural unemployment.
Osberg, Lars. 2005. "COMMENTARY." Economic Policy Review - Federal Reserve Bank of New York 11(1): 19-22.