Chris Dwyer, Sr Research Analyst with the Aberdeen Group, just published his survey findings in a report titled The Next-Generation Guidebook to Contingent Workforce Management
. I had a look and thought his findings were very insightful. I also found it interesting to compare his findings to the work done by HR.com's Institute for Human Resources - Contract Workforce and Talent Exchange who commissioned Elaine Orler to conduct a survey. Her findings are included in the link to the white paper below. I'd encouage you to have a look at both.