When one opens a question and starts typing a title, a list of possible duplicate questions is shown as illustrated below.
I assume that this isn't used often since some quite obvious duplicates are still created on Super User. Perhaps a "I checked the list and it wasn't there" checkbox could be added to solve this.
Moreover however, I'd like to be able to fetch this list when viewing an existing question. I think it'd allow the higher rep users to locate and assign duplicates faster and more efficient. Checking for duplicates now consists of searching a duplicate while this would be much quicker. Furthermore, it might decrease situations where users answer a question without realizing that it already exists and thereby encouraging duplicate questions, which has been discussed at length here.
For example: Add a link (Find possible duplicates) next to "close" and "edit" that will open an overlay div (Like the closing reasons div) and display the same list as above.