The way in which consensus works at Shepard is like so: all hall decisions are made at the weekly hall meeting. This meeting is arbitrated by the "HeDaShe" (a word play upon the gender neutral he-dash-she), which is a rotating office, filled by a different house resident each week. The HeDaShe is not only responsible for compiling an agenda (although residents are responsible for bringing their concerns to the HeDaShe well before meeting time. While meetings can be flexible, they can also become bogged down and tedious), but for maintaining order during the meeting (through recognizing speakers, asking for decisions, and so forth). It is up to the HeDaShe to make sure that the meeting does not drag on, yet to make sure that everyone has a chance to make their point clear (while gently censoring repetitions of previously made arguments).
When an issue is to be decided upon, it is first described by whoever brought it to the HeDaShe in the first place. Then, arguments are heard on all sides. Once the various considerations have been outlined to everyone's satisfaction, a consensus vote is taken. If it passes unanimously, then good. If it fails unanimously, good. However, if it is not unanimous, anyone who dissents may explain why they have chosen to, the floor is again opened for discussion, and the process repeats. Of course, if it becomes obvious to the HeDaShe that their is no chance of compromise, s/he may elect to simply remove the item from the agenda, for discussion at a later date.
Consensus lies at the heart of Metanoia; understand one and you'll have an excellent grasp upon the essence of the other. The art of consensus is the art of communication and compromise.
Please see the relevant passage from the Metanoian Constitution.
More information about Metanoia is also available.
James "Eric" Tilton, Self-Appointed Historian of Metanoia, tilt+@cs.cmu.edu