Now that the site has gone public and new members are joining, we will have duplicate questions. How should we handle them? Is it the moderators' job?
Under every question, there is a "close" link:
When you click it, you are presented with a set of close reasons. One of them is "duplicate of...":
Once you choose this option, you can search for duplicates or directly insert a link to an existing question.
Once there are 5 "close" votes cast by site members, the question will be closed and a link to the original question added to its body.
Note that there is a certain reputation level required to cast "close" votes. Currently, it is 500, but it will be increased to 2000 once the site graduates from the beta.
In case you haven't reached the necessary reputation level, you can instead flag the question for moderators' attention.