As an aside, is there any particular reason that the comment header (containing the commenter's username and other details) was designed to be grey and of the same text size as the actual comment body?
I think we can say that standard forums are much more 'scannable' compared to HN, and I often find myself looking out for posts from users whom I respect on that particular forums. In this case, Putting the username before the the points of the comment may lead people to view the comment for the commenter first and foremost, as opposed to the number of points the comment has.
I don't know whether or not that is a good thing. For one, it makes negativity very obvious, and it makes recognising a bad commenter pretty easy.
On the other hand, it may give a free-first pass to 'respected' commenters who might make mean comments every once in a while.
On the whole though, I think it may make it easier for your average user to recognise and avoid mean comments when they do see them.
Another possibility may be to shift the position and/or size of the upvote/downvote buttons to make upvoting a more conscious decision. I've got no suggestions about how to do this yet though =(.