Duplicates seem to be one of the bigger issues for me when looking for answers. Many people also seem to ask questions without first looking for duplicates (I appreciate the irony that someone will probably find a duplicate of this very question and flame me in the comments; however, that just proves my point).
It would be great if there was one of the following to encourage less duplication. I'd be for losing reputation if enough people flag and agree that a post is duplicative (with citation). Also, give badges (reputation) to people who find duplicates and enough people agree on the duplication with the same citation.
In order to preserve the duplicates, have a duplicate section/button that will show in a threaded manner which posts have been considered by the community to be duplicates. This way, the duplicate questions at least aren't lost. The best part is the highest rated questions of the duplicate set can then be the master question for the duplicate set. The best answers would then be aggregated across all duplicate questions.
Sorry if this question is actually a duplicate.