I would have thought google wave might be a good fit for this. Or even a wave plugin if you require something more specific, like the 'accept/reject' feature?

I would have thought google wave might be a good fit for this. Or even a wave plugin if you require something more specific, like the 'accept/reject' feature? Concept Draw Office also offers something like it.. integrating brainstorming, mindmapping and project management in one suite.