Here is a link to a slashdot report about a Fortune 15 company asking employees to sign a social media usage agreement.  The agreement seeks to ensure good behavior on the part of the employee, according to the report.

http://tech.slashdot.org/article.pl?sid=09/05/12/1818245

Two main ideas come to mind: 1. Hire the right people and you don’t have to worry about their off work employment. 2. Deal with corporate issues correctly and take care of your employees and then they won’t have cause to dog your company out on facebook or twitter.