Here's a suggestion: figure out the 'topic' words in the subject (shouldn't be too hard to do a moderately good job by looking at word frequencies in the titles submitted so far and whitelisting/blacklisting some); start attaching a penalty to each topic word based on how many stories were submitted recently, how many votes/comments they got, and a time decay. The goal is to make it so that a story about a very frequently seen topic will need more upvotes to climb higher in the rankings.