This is an interesting development in the world of temporary and contract workers.  Bear in mind, once you become a W-2 that changes the composition of your business as a self-employed individual.  Examine the pluses and minuses before making a switch like this.

Outsourcing Firm’s Latest Offering: Health Insurance – BusinessWeek

Switching to services like oDesk Payroll has tax implications for freelancers as well. While workers who switch will no longer be subject to the self-employment tax, they will also lose many of the deductions they claim as contract employees.