I would like to see the ability for users to mark questions as duplicate. I find (at least in the section I browse) a lot of questions that are duplicates and potentially left alone with no answer. Some people use different verbiage than others so marking a question as duplicate will link future searchers to the "answered" question.
Hopefully this Idea isn't a duplicate in itself
The same rules for having the ability to set a question as duplicate could be similar to the way Stack Exchange does it where moderators or those above a certain threshold can mark questions as duplicates.