Wendy Harman at the Red Cross has been hard at work creating this draft version of the organization's Social Media Strategy Handbook. It is intended for staff and chapters and is encouraging them to participate in social media and craft a strategy for their chapter. It isn't a command and control policy, it's encouraging, provides a lot of useful tips/steps, and is also realistic about the time commitment involved.
The first step is to become social media savvy - the premise that you can better understand how the tools work if you use them personally. It goes on to lay out some guidelines for personal use if the employee or volunteer chooses to self-identify their affiliation with the Red Cross.
The handbook is built upon the work of other organizations that have shared their policies.