The comments so far refer to the "sentiment deducer" aspect of the service. They've brought up some examples of how it's not working right now, but they missed an important question: what in the world is "positive sentiment" abstracted from context, and why would I want to know if a site had it?

An issue we haven't brought up is tags. Current tags for HN: "ago, points, comments, com, hours, hour, hacker, discuss, minutes, tornado." I see some good ones, but it's quite noisy (and it seems to have grabbed the tornado story as a main topic--scraping the title?). This feature seems most useful to me, and most easy to improve.