I've been using TeX.SE for some time now, both for questions and answers.
Although I do flag a new question as duplicate if I know that question has been posted before, I often find myself tempted, in a crave for reputation, to quickly answer a question (if I can) without checking beforehand whether it is a duplicate.
Perhaps I need professional help; TeX.SE can be so addictive! However, I suspect I am not the only one to feel and act that way.
As someone about to answer a question, should one always check whether the question is a duplicate?
Do you feel, as I do, that the reputation system can prove counter-productive regarding flagging questions as duplicates (when they deserve it)?
EDIT: I unearthed, in SE podcast #15 (starting at 11'20''), a discussion between Joel Spolsky and Jeff Atwood that is relevant to the topic.