We have an outsourced social media person here where I work, because nobody here has time to manage daily posting on all of our FB pages, Twitter, etc. We drive the overall strategy and campaigns, and this person does the legwork. They also do some research/brand monitoring for us to find places to do media buys.
That being said, a lot of the "social media gurus" out there will do nothing more than set you up with a custom FB/Twitter page and leave you to manage it/charge top dollar to do it for you. These gurus usually have no idea on how to actually build a community and convert it to sales.