As Henry Jenkins said it right:
YouTube represents a shift away from an era of stickiness (where the goal was to attract and hold spectators on your site, like a roach motel) towards an era where the highest value is spreadability (a term which emphasizes an active agency of circulation of media content)
However, question remains: what does that mean exactly? If the importance of the source somehow loses its cool and content flow itself is all that matters, is medium no longer the message? What are measurable parameters of legitimacy, credibility, and authenticity if stickiness, and therefore the source site, no longer counts. Social graphs, data portability and data-driven journalism are no longer futuristic terms for the early adopters, but everyday concepts that determine current online business models and influence the chain of economic value added, especially in the media industry.
YouTube, being just one example of how spreadability is the prevailing currency of success, already demonstrates in how far content is king and, agency is, to stay in chess terms, just a poor pawn on the battlefield of attention. The agent, now nothing but a messenger, is crucial to the success of spreadibility (e.g. of a video). Consequently, the network of the agent is pivotal for the intended outcome. Examples are apparent not only in the news (e.g. Hudson river incident), but also in advertising (good ol Spice) and the music biz (Soulja Boy, just to name one internet phenomenon).
So, I guess in the future we will see whether impactology of the agency or the spreadability of content will prevail.