The German Pirate Party created Liquid Feedback over a year ago to allow party members to debate and decide on their platform and other issues. They have been using it successfully. Here is a video explaining it (in English):
On Sunday, 7/1, I will be helping with the Massachusetts Pirate Party's hackathon to get our own copy of Liquid Feedback running. We will start at 3pm and will go until we are done or until asked to leave, whichever comes first. The hackathon will be at 45 Bromfield #2, Somerville 02144.
Please sign up if you want to help so we know who will be there.
If you cannot make it in person, then you can join us on the #masspirates irc channel at pirateirc.net. We will also post our progress at the #masspirates twitter hashtag.