Bayesian ranking of items with up and downvotes or 5 star ratings
I've always considered "bumping" to be the perfect scaling algorithm for content sorting. If a comment is added to a thread, it will show up at the top of the page until a comment is added to another thread. Thus the probability of seeing a thread on the front page is proportional to the responses it gathers. New threads will be seen immediately and will generate responses if interesting. Unpopular threads will still get a small chance at reaching someone rather than never being seen by anyone. Finally, two threads that would otherwise generate equal number of upvotes or stars would be scaled by how deep and worthwhile their content is, since a simple like is less meaningful than a like and a long comment.