Top Books on Amazon Based on Links in Hacker News Comments
I did something pretty similar over christmas, though I used named entity recognition to extract book titles rather than looking for amazon links, and (so far) also limited it to specific "Ask HN" threads about books. You can find it here: http://www.hnreads.com/. It is interesting to see how little overlap there is between the two, though that may be due to my using far fewer (and also newer) threads!