This is thinking ahead a bit, but since most of these questions are subjective, there's a couple situations we'll eventually have to deal with:
Questions with changing answers. For example, if someone asks "What's the hottest new language" today and then someone else asks that in a year or two, is it fair to mark it as a duplicate? At what point is it ok to repeat time-sensitive questions?
Very subjective questions (eg, "What's your favorite programming joke?"). Such questions get filled up pretty quickly and then stagnate. Do we want to always point anyone wanted to ask that to the super big, super old original question, or do we eventually want to allow it to start over and let new users contribute?