One thing I wonder about is whether accumulating personal karma is a red herring: trolls don't seem to care about their karma, and good folks may not care either. Perhaps the most important thing about upvotes and downvotes is how they affect visibility. Everyone wants their voice to be heard, and some people want the opportunity to influence whether other people's voices are heard or not, e.g. by flagging stories or…
This data is interesting because now if you randomly perturb the front page, say by putting a new story in position #5 and lying about how many points it has. Show this perturbed page to a small sample of users and see if the story beats the historical averages or not.
If that kind of thing worked, it could help correct for the phenomena where a popular story stays popular just because it's popular. You can now rank stories by how well they take advantage of their "real estate" on the front page. Those that underperform the average sink, those that outperform the average rise.
One hitch. This might not work if you tell people you're doing it.