Frome the Economist: "Paul Saffo, a futurologist and one of the world's most enthusiastic technophiles, also looks at the downside. “Each of us can create our own personal-media walled garden that surrounds us with comforting, confirming information and utterly shuts out anything that conflicts with our world view,” he says. “This is social dynamite” and could lead to “the erosion of the intellectual commons holding society together...We risk huddling into tribes defined by shared prejudices.”"

Most of the tacit knowledge spitten out in Blogs and so On is OPINION!.

jk ..but...
Now for the optimists: Lee Rainie, the director of the Pew Internet & American Life Project, a research foundation, believes that “people will become not less but more aware of differing arguments as they become heavier internet users,” because contradictory views are just a hyperlink away. A survey by Pew appears to confirm this view. Mr Anderson of “The Long Tail” says that “opinion is a marketplace, and marketplaces work when you have liquidity.” Liquidity is exactly what participatory media provide

https://www.economist.com/surveys/displaystory.cfm?story_id=6794256