Joe Marchese of socialvibe has a great Mediapost column on why social media agencies will become the new Agencies of Record for brands.
I take his prediction a bit further in my comment to his post:
Social is becoming the central hub that connects marketing, customer support, product development and reputation management. This is a primary change in the way companies interconnect with markets and customers and the new agency of record has to be prepared to wade into all of these business divisions and unite them. My guess is we’re going to see an entirely new agency model emerge that is not hampered by the silos you describe. Among our customers we’re seeing the early adoption and growing understanding of this new nexus- and interestingly most are either PR or ‘digital’ agencies. Very little uptake with the media-focused agencies so far. As with PPC/SEM/SEO adoption, they tend to lag a bit in adopting new models. This time around lagging could prove disastrous because the move into social media is happening very quickly