I jumped right on Craig Canning's
VAclassroom course in social media marketing when he offered it recently, and am now offering services as a 'specialist.' As a writer, it seemed the most direct way I can serve small businesses, helping them present well online.
Actually, it seems to me that in another 5-8 years everyone will be so well-versed in navigating social networks online that they won't need guidance; but there will always be a need for those who can sub-in for the business at social sites, do the writing and distributing and tracking, etc.
In a way, it's almost a basic skill that any VA might be likely to offer, like desktop publishing or database management.