slightly off-topic, I guess but... I think that checking if the same 'topic' (page title, main keywords, etc) has been posted may be more important. After all,

slightly off-topic, I guess but... I think that checking if the same 'topic' (page title, main keywords, etc) has been posted may be more important. After all, even if nobody posted yet the URL I'm looking at... but if that URL is a brief blog post linking to another blog that passes through to the actual story... and if that story has been posted to HN... then I might as well add the URL I was looking at in a comment. No?