Reason Foundation: 2008 Annual Privatization Report
Of note, they found that taxpayers were saved $7.2 billion over the past five years through federal competitive sourcing. From the press release:
Competitive sourcing allows the private sector to compete for jobs and contracts that are currently performed by the government. Federal employees actually won 83 percent of the job competitions from fiscal 2003 through fiscal 2007. But taxpayers are the real winners: the Annual Privatization Report shows taxpayers save $25,000 for every job that is put up for competition because even when the government keeps the job it significantly improves efficiency and reduces costs.
You can view the whole report online here.