Let me hope that this is not a duplicate, as I've did some research and havn't found something that is exactly the same!
As I'm getting more "used" to StackOverflow way of working, I'm doing more and more reviewing.
And, like everybody, you always fall on question which is an exact duplicate of another question. Sometimes by new user and sometimes by ancient users. Most of the time the question gets marked as duplicate and finally close.
The thing is that, the user still gets reputation. I do agree that may be the question was well formatted, and writen in a correct english, but as the downvote states
does not show any research effort. As it is a duplicate, and if I can find it is a duplicate, then the OP could have prolly found that its answer was already asked and answered. Lets take the case of a new user, that ask a duplicates that I saw today. I did down voted really fast and flagged/commented as a duplicate in order that other people see it also, but still he managed to get 5 upvote for his question. Well that's nice for him BUT we are encouraging a BAD behavior that is not doing research before asking.
I do understand that sometimes those duplicate will add some information not present on the other question, but still make the site harder to maintain and spread the information at more places.
Should the reputation gained on duplicate question be kept, or should the OP rep gains on that question be cancelled? I mean that would show that we, at stackoverflow, want people to do some research first, before asking for help. At least if the person do some research AND find the duplicate than still needs more information, he can put a link to the other question saying it is closely a duplicate but that it lacks this or that information.
Should all the rep gained on answers be kept also ? Or should it be halved or I don't know? Because I don't think removing it completly is a good idea since it could discourage user from posting answers some time.
Should there be gain for flagging duplicate (small) as it would encourage user to do the research job to close them duplicate and clean the site more?
I think that this is a big issue as there are a lot of duplicate question and probably a lot of "ghost" duplicates as they are not found since you don't always have time to do deep search of the site as reviewer (or whoever wants the keep the site clean) to find them. And maybe giving incentive would the clean.
Here is an example that I've reviewed yesterday.
There are some question which are related but are kind of old, and I think this is a debate that is still actual, and should get more attention.