Thank you, although not everyone agrees. Although sometimes they then get re-upvoted, many of the duplication notifications get downvotes. Here are two recent ones:

http://news.ycombinator.com/item?id=2392849

http://news.ycombinator.com/item?id=2392739

That's baffling to me, because I almost always click-through on the previous discussions. Maintaining discussion history adds value to the community.