Also, they use hacker news to communicate to applicants. I applied a while back, and one day while browsing I got a message through HN, something like "pg has a question for you" in the header bar. Clicking through is the question, and place to put the answer.

Basically, there's a whole messaging system in hacker news that most people don't see.

Yeah, this is known :) but an algo that incorporates HN karma wouldn't be the best thing :P