Yes, I care, as a form of trust metric: For the person: it is a simplest way to see if you fit or not in this community. For the community: quickly judge if the post or comment is spam or not.
I totally disagree. The best way to judge if a post is "spam" and if someone is a "spammer" is based on the content. I downvoted your post because it both is a poor form of reasoning and it is needlessly alienating to others. I don't downvote often, and I don't have anything against you, but it is important that everyone, especially the lurkers, feel welcome here. My downvote is to show you don't speak for all of the…
Content based filtering is extremely expensive, just look at email. Reputation based filtering is quick and easy both for people and computers, but it has its own drawbacks, I agree.