Reposted from a Comment. Not exactly what I would say if I was writing it from scratch again but the points are all there.
David Graeber was right in this interview when he and other veteran activists worried that the General Assembly might not work, since the model that had been used in the alterglobalization movement had been based on Spokescouncils, which are meetings of delegates of pre-existing organizations and affinity groups.
Anarchism assumes collective rather than "mass" organization. In a Spokescouncil form or organizing, the various groups/organizations/communities that are concerned about a shared problem or that have a shared goal all send delegates (Spokes) to a meeting (Spokescouncil) where the decisions of each group are reported to each other group; the delegates then report back, new decisions are made, and the Spokescouncil is held again, repeating until consensus is reached.
This is a Federation form of organization- each group is autonomous and may leave at any time. The federation as a whole only exists under specific, mutually agreed-upon, and clearly state principles (i.e. "the purpose of this group is to prevent a nuclear power plant from being built at this location" or "this group rejects violence and property destruction"). These principles form the basis of when Blocking is legitimate- if a proposal violates a principle, either the proposal should be blocked or the principles should be amended, either of which may mean a split in the organization.
The reason Occupy Oakland (and the Occupy movement as a whole) is so dysfunctional is that it's not using Consensus but rather some weird amalgamation of several different systems. If it was instead a federation of the various communities and organizations based on particular philosophies or strategies, then it would be easy to kick out anyone who doesn't adhere to the mutually agreed-upon principles (which, incidentally, haven't been written)- to kick someone out, you just stop working with them. What they do is their own business.