It always seemed to me like the list of up/downvotes forms a graph not unlike hyperlinks the web; I'd be curious to see a site that tried to apply a PageRank-like algorithm to that graph rather than a pure "one vote = one point" system like reddit.
Of course this would probably lead to SEO-like techniques and attempts to game the system, and high-karma accounts would probably end up being sold for cash, it might encourage groupthink, etc, but it still would be interesting to see how it rolled out.