From Marketing Experiments Blog:

If you're like many companies, you might think outsourcing social marketing is your best bet.

But more than ever companies are working to keep social media in-house because it requires such an intimate knowledge of the brand and because of the personal nature of social media interactions in general. Customers want to talk to  you, not an "outsourced" spammy twitter account. And when you leave them with no choice, they happily take their discussion to your nearest competitor.

…

Instead of hiring or tasking the best person for the job, whether that's managing the Twitter account or actively engaging in forum discussions, many companies put their least experienced, least qualified people on an overwhelming number of social media initiatives. Usually this person is in marketing and may be tasked to cover topics or areas of social media they have little or no experience in. But this isn't the most efficient and certainly not the most effective method for achieving social media success.