The NFL doesn't allow players to post to Twitter, Facebook and other social media sites at certain times on game day.

The US Marine Corps has banned access to social networking sites from its network.

Companies take such measures when it comes to social media to prevent information from being leaked by employees, even inadvertently. Other companies are concerned about security risks that may come from these sites.

In a recent blog post on News Channel 9's Web site, Latricia Thomas writes: "Businesses big and small are using social media to communicate outside their four walls. But that scares some people. They fear unfettered, unmonitored communication involving their staff, their products, even company secrets."

Thomas also quotes Brian Uzzi from the Kellogg School of Management at Northwestern University, who understands that accidental information could be posted and then "could propagate so quickly that it doesn't give the corporation a chance to manage people's impressions about that leaked information." But Uzzi also explains that employees could feel they are being limited by some social media policies.

Over at Erickson's Blog on Social Networking and the Law, Megan Erickson wrote a post about how employers should think about their social networking policies. She brings up the IBM Social Computing Guidelines, which was one of the first such policies to be publicly available. But she cautions employers that what works for IBM may not work for every company, and you need to keep your own company's business needs in mind. "More than 10 years ago, when most employers were trying to limit employees’ online activity, IBM was encouraging its employees to use, learn and participate in online activity; the company continues to advocate its employees’ participation in Web 2.0. The overarching business interests of a technology company like IBM (i.e., promoting use of online media for marketing and business reasons) may conflict with the overarching business interests of other employers (i.e., perhaps a greater need to protect proprietary business information)," she writes.

So where does your employer stand? And what would be the tipping point for you before your company's social media policy becomes unacceptable?