Another nice opinion article which cites the tendencies of "flat" organizations to create opaque hidden hierarchical political structures, with some references to Github, Valve, and 60's commune and feminist groups.

http://www.wired.com/2014/03/tyranny-flatness/

  Critics say flat organizations can conceal power 
  structures and shield individuals from accountability. 
  This idea dates to the 1972 essay The Tyranny of 
  Structurelessness by Jo Freeman, who describes her 
  experiences in “leaderless” feminist organizations in the 
  1960s. “There is no such thing as a structureless group,” 
  Freeman wrote. “Any group of people of whatever nature 
  that comes together for any length of time for any purpose 
  will inevitably structure itself in some fashion.”


  The problem with supposedly non-hierarchical groups, she 
  wrote, is that power structures are invisible–and 
  therefore unaccountable. That inevitably leads to 
  disfunction and abuse. Charismatic leaders could use their 
  position to advance their own agenda, award desirable 
  tasks and projects to an “in group,” and shift blame for 
  mistakes.

and more on Valve's flatness in practice, http://www.wired.co.uk/news/archive/2013-07/09/valve-managem...