I'm sure this has been around for a while, but I've only just seen it. It's not been used much by the look of it, and it's design usability could be better.
But have a look - click on the pic on the right of the site (currently Tony Blair) to see what they have in mind.
I've often thought that a 'debatewiki' would be a good idea, though it would be a bit labour intensive...
(ta for the tip Alan)