Few Companies Have Policy for Employee Use of Social Networks | eMarketer

Worldwide, only one-fifth of the companies surveyed had a formal policy for employee use of external social networking sites. Firms in the Americas and Asia-Pacific were somewhat ahead on this front, but the majority of respondents in all regions had no policy in place. Among companies that did have a policy, 63% claimed it was effective in combating lost productivity.

via eMarketer

There is still a lot to do: Social Media Guideline are in my opinion a must.