Bitcoin is the first "voluntary consensus" system I think we've seen. Other systems may be centrally decided or democratically decided, but in all cases once a decision is made you have to follow it. For example we have:

• The FED - Small group of people make all decisions. No one else has any influence over said decisions. Once a decision is made, everyone is forced to follow the FED's decisions or go to jail.
• Democracy - Large scale popularity vote, everyone gets to include their voice (in theory, we all know there are problems in today's "democracy"). Decisions (in theory) follow the opinion of the majority. Once a decision is made, everyone is forced to follow the decision or go to jail.

In both cases, once a decision is made you have to follow it or go to jail.

Then enter bitcoin. Everyone gets to choose which system or path to participate on. There is some form of centralized decision (the devs) but people are free to ignore them. Decisions also come down to a large scale popularity vote of sorts and most will follow the economic majority.

However there is no requirement to follow either the devs or the economic majority. Any group of people can tell the rest to f'off and follow their own path. They will be isolated and excluded from the majority, but they are not stopped and if later proved right the majority might just come back to join them.

This is unique as far as I can see, I am looking forward to seeing how the 20MB fork plays out largely as the first real test of how well "voluntary consensus" works in practice.

200 years ago the very idea of trying democracy was considered a "grand experiment" (one that many predicted would fail). I think a key failing of democracy however is it is still binding. Today "voluntary consensus" is the grand experiment.