I have noticed comments on another HN account being consistently downvoted, once or twice, about 24 hours after they were posted, regardless of the comments' content and the subject matter of the OP. This has been going on for several months.
There may be a number of reasons someone or some group of people would employ this tactic, but is it "fair game" with respect to HN's policies and the sensibilities of HN's readership?
I know this is all rather meaningless, but something about it is very upsetting to me and I always upvote such comments.
On that note, I like the Stack Overflow model: you have to pay reputation to downvote.