Here are some best practices to help avoid legal issues in using social media:
Do not copy other people’s content without express permission to do so.
It is generally permissible to link to other blogs or websites. However, you should ensure that the blog or website that you are linking to does not infringe copyright.
If you have employees saying great things about your company on their personal blogs or anywhere else, they need to disclose that they are employees or are getting paid to write the reviews/endorsements.
Get releases for the use of private information/pictures and for celebrity materials.
Register any copyrights and trademarks so that you can enforce them both through Facebook, Linked In, etc. policies and in Court.
Make sure that your staff/employees are aware of these issues; you are liable for what your employees do!