I'm really, really hoping that you're logging referrer data along with scores - if you're not already, you might consider starting. Even if this is not a source of proper scientific data, it would be highly interesting to see how, for instance, the Reddit referrals do vs. HN vs. Facebook, etc. We can probably all make some fairly accurate guesses about where the high and low performers would come from, but I'd be real curious to see the exact breakdowns.