If you knew everyone’s opinion on everything, you could extract lots of useful information from the correlations. So maybe there should be a Web 2.0 thing that let users answer a lot of controversial questions and maybe display them in a profile.
Then you could let people query it based on user-defined criteria. (“Among people over 50 who believe in string theory, who’s considered the favorite to be Cthulhu’s running mate in 2012?”)
You could also try out many algorithms to figure out which one best turned opinion data into the right answers to objectively scorable questions. (“What will the temperature be in a year?”) Then you could apply that algorithm to answer all other questions.
Potential problems abound. For example, objectively scorable questions are a biased subset of all questions. Methods used to extract the most reliable answers to them may not generalize. Also, there would be “strategic voting”-type issues.
If these problems could somehow be solved or contained, the result would arguably the most authoritative source on Earth, and a new argument for majoritarianism. (I picture it coming with the sound of a booming voice saying, “you dare disagree with Authoritron?”. That way it will reduce irrational overconfidence in one’s personal opinions. Social psychology, etc.)
(This is a similar idea but with the intent of fixing inconsistencies in an individual set of opinions rather than using other people as authorities.)