Just made this suggestion to Yahoo. Maybe others should as well.
There are a lot of people in the message boards that will make a simple comment on posts from long ago, sometimes over a year ago, simply to make it jump to the top of the list. One person in particular has the name Loboosh. But, I would like to have a settings option where I can ignore posts that were originated more than "x" amount of time ago. Say, I would be able to set it where if somebody comments on a post that was originated more then a month ago then it wouldn't move to the top of my list.