I don't mind duplicate posts. Really. Most lurkers do just that, they lurk. And when they feel the overwelming urge to post a comment they do that. Most people do not search for articles, they just start at the top and go down. They'll look at the right hand side bar to something that may be headlined and then they look at recently posted replies to see what everyone is posting. Then they get off FR. Or go do something and come back.
Since most people don't do searches for a specific article, it's not bad to have a something posted again. Besides, if the conversation has taken a bad turn, like when two people start flaming each other about a stupid point that doesn't mean a hill of beans, it's kind of nice to not have to keep tripping over them.
DOUBLE POSTS ARE NOT THE END OF THE WORLD
If you are surfing the web, and find a news item that is worthy of posting, and then come here and discover it's already posted, then the best thing to do is merely bump the original thread, which due to your hard work is already at your fingertips. Not only does the rest of the forum get a chance to see all the earlier comments on the original post, but someone who missed the thread the first time around is equally likely to see it than if you went ahead and posted the whole article over again. Plus, you get the occasional satisfaction of resurrecting a dormant thread. [my 2c]