The point isn't to determine if you will like a post by applying sophisticated language processing etc. Its to determine if you will like a post by looking at the people who have upvoted/downvoted it and learning how to extrapolate.

For example, suppose Alice always upvotes/downvotes identically to Bob. Of particular interest to Alice are posts Bob has already upvoted. In real life you are looking for significantly more subtle patterns (if you only looked directly at correlations between users' feedback you wouldn't get too much advantage, at least not in theory) and you need to be able to do it automatically and quickly, but hopefully it seems plausible that you can use the pattern of upvotes/downvotes to practically and effectively predict what will interest any particular user or the average guest.