Why downvote? I honestly do not get it. 
Mathnerd314: It might be interesting to keep every vote for each comment and use something like the Netflix prize algorithm to calculate whether you'd like the comment. Hiding comments would then be based on personal preferences, rather than the community at large. If nobody at all likes the comment, (i.e., it's spam or something), then it can get removed automatically. Of course, this takes a lot of work to implement, and it might require HN to have a longer privacy policy...