Which department should own social media?

Many presentations from Monday's primer discussed the involvement of various departments in the launch of online communities. The speakers were community managers who had the benefit of working across departments while staying faithful to the communities they served. They limit marketing messages, engage the proper resources when necessary, set up guidelines and manage the health of the community. Companies instinctively think that marketing and communications should own social media, largely because it is seen as another channel to convey the marketing message. However, I heard today that many believe that companies should limit marketing involvement in social media in order to foster the relationship without appearing disingenuous. If you don't have the resources for a community manager who do you think is best suited to own and cultivate the user relationship?