The fear might be that if it was public that (say) 25% of Republicans want the troops home the looney fringe would target all Republicans as probably traitors.

I think it's an interesting idea, and one that I might suggest to our local hippy anarchists, I mean "Green Party". As a way to reduce political conflict over ideas that will never get off the ground I think it has some merit, and on a small scale like that I think it could be done simply using OSS and a publically visible server. Almost by definition organisation members already trust at least some people running the organisation (the intersection of the sets of trusted members might be empty, however).

It would be good for situations where there's broad cross-party support for something but not a majority within the government. It would be tricky for party based states - the UK/Oz idea of parliamentary whips and forced party votes could mean that even measures with enough support would fail to pass (there's often more than a simple majority required to get a free "conscience" vote, if not outright "only with permission of the dictator, I mean "prime minister"). This is where non-repudiable votes would be good, but of course they would be mostly useful when they threaten the interested of the most powerful so I suspect it'd be like campaign finance reform - lots of supportive talk but no action.

I doubt the "option" of revealing the members after a certain time would really be optional - with advances in technology any valuable list would probably be cracked after a relatively short time. OutTheBastards@Home or something similar would show just how strong geek community opposition to some proposals is. Ditto for any security by obscurity solution, where leaks are inevitable.