It seems like the latest media debate is who really owns social media – the agency or the client? Obviously there are benefits and negatives to one or the other running the show. In my opinion the answer to the question is BOTH the client and the agency should be in charge of social media.
My thought process is if a brand is working with an agency for their marketing needs than as an arm of the marketing process, social media must be addressed on both the client and agency sides to ensure that all messaging is aligned. Due to social media relatively “new” presence in the marketing and branding processes many clients find it time consuming and do not feel that they have the ability to take it on and be considered relevant without a dedicated resource. As the Director of Social Media, this is where I feel a person in my role can be most beneficial to a client – I have both the knowledge of the social media platforms and the understanding of the clients messaging (which is handled by the rest of the firm) to work hand in hand with the client to create an agreed upon social media message and strategy that matches their existing marketing efforts.
This article from MediaPost is a great read on the subject – http://www.mediapost.com/publications/?fa=Articles.showArticle&art_aid=119450