The oft-repeated comment that social media/networks are time wasters is one that needs to be dispelled with facts. When employees waste time it is not the tools such as social networks that are the culprit. It is a symptom of ineffective management. Employees have found a myriad of ways to waste time long before social networks, or emails, or the internet ever existed and they will continue to do so when they are not fully engaged, are not committed to the success of the organization, are not a good fit for the culture of the organization, do not have enough to challenge them in their work period, or have not established a solid work ethic. None of which requires a social media tool to create a problem, but all which does require good management and leadership skills to fix.
Internal social networks are used very effectively by several organizations to share information about products and services and projects; to share knowledge among co-workers that enhance customer service and enhance employee skills; to retain knowledge in the organization when employees move on; to improve overall communications especially in geographically diverse organizations. External social networks are used for marketing, resolving customer issues, sharing promotions/sales etc.; establishing a brand etc.
The thing about 'social' as a business or organizational tool is that it requires research and education to fully understand what it is and in what ways it can help or potentially harm an organization. I strongly recommend that people really do explore it carefully in order to understand it. The potential is amazing-and whether a business ignores it, bans it or embraces it-it will affect the sustainability, reputation and success of the business.