On my to-do someday list is a site for recording and organizing debates. Arguments would appear as boxes of text, organized into a tree structure. Opposing arguments could be added as children to a parent node. Arguments could be filtered by up/down voting or some other system. Debate trees could be searched. Etc... Somebody really should make this. I remember messing with some Flash site somewhere that did something…
Something that can automatically categorize the blogosphere discussion - e.g. who's agreeing/who's disagreeing (what's the median level of agreement/disagreement). I'd like it for the sole feature of finding/filtering out the (sometimes useless) echo-chamber opinions - to surface the divergent disagreements/opinions
User-originated voting is good but combining it with intelligent algorithmic appraisal (what they are voting by what they are saying) might be interesting