(the following isn't off-topic, I promise:)

Attention, people who have a lot of free time and want to found the next reddit:

When a site user upvotes and downvotes things, you use that data to categorize that user's preferences (you'll be doing a very sparse SVD sort of operation under the hood). Their subsequent votes can be decomposed into expressions of the most common preference vectors, and their browsing can then be sorted by decomposed-votes-with-personalized-weightings.

This will make you a lot of friends (people who want to read ramblings about philosophy won't be inundated with cute kitten pictures and vice versa, even if they use the same site), make you a lot of money (better-targeted advertising pays better), solve the problem above (people who like and people who hate trollish jokes won't need to come to a consensus), and solve the problem way above ("predisposition towards rationalism" will probably be one of the top ten or twenty principal components to fall out of your SVD).

It will also create new problems (how much easier will it be to hide in a bubble of people who share your political opinions? how do you filter out redundancy?) but those can be fixed in subsequent steps.

For now it's just embarrassing that modern forums don't have either the same level of fine-grained preferences that you could find on Slashdot 15 years ago ("Funny" vs "Informative" etc) or the killfile capabilities you could find in Usenet readers 25 years ago.