Hypothetically, if I could access only the sites visited by the HN crowd, that would be fine by me. Somebody in an art community might feel similarly. If there were some metric the crawlers could use to rate a page (time spent on page, manually downvote, etc), then the signal/noise ratio would be really good.
Obviously if I wanted to do a really broad search, I'd use a typical search engine, but if it's tech related, I wouldn't mind pages that have been browsed by HN.