Dupe. This was discussed at length (144 comments!) back in March. I remember because a) I mocked the pathetic "It so happens that advertisements are devastating to my well-being." statement and got voted up, and b) a swarm of pro and anti ad blocker posts hit HN over the following 24 hours. It was almost as fun as the iPad launch.
Does flagging even work on HN? This seems a prime candidate so I'd have assumed it'd have picked up a fair number by now. We're seeing not only a dupe link, but a dupe discussion too!
Added: Aha, here it is: http://news.ycombinator.com/item?id=1172302