Very interesting post by John Battelle on why the LA Times edtorial wiki failed.
But when I read about this, I instantly recognized a core problem with the approach: it was top down community, rather than bottom up. Michael Kinsley, who created the site for the Times, was attempting to force a considered, editorial structure onto a set of readers who had yet to identify themselves or their own interests in any kind of structured way. It was doomed to fail, because communities can't be created by editorial structures - editorial structures must be created by communities.
Also Dan Gilmour on same.