When you build a system where you get points for the number of people who agree with you, you are building a popularity contest for ideas.

However, your popularity contest for ideas will not be dominated by the people with the best ideas, but the people with the most time to spend on your web site.

Votes appear to be free, like contribution is with Wikipedia, but in reality you have to register to vote, and you have to be there frequently for your votes to make much difference. So the votes aren’t really free - they cost time.

If your popularity contest for ideas inherently, by its structure, favors people who waste their own time, then … the most popular ideas will not be the best ideas … The people who have the best ideas, and the ability to recognize them, also have better things to do and better places to be.

http://gilesbowkett.blogspot.com/2008/05/summon-monsters-open-door-heal-or-die.html