I don't think anyone's suggesting that, or anything sufficiently like it to warrant concern.
The behaviour I'm talking about is: A goes through all B's old comments, systematically downvoting a few of them every day for some time. Not selecting particularly bad old comments, you understand; the comments themselves are irrelevant. The only goal is to be able to reduce A's karma by a lot more than a single downvote would, without making it too blatant what you're doing.
(Why old comments? 1. So it's less obvious to anyone other than B what's happening. 2. Because A has already downvoted all B's recent comments.)
Do you think this is a "useful function"?
Well, you're talking about the state of mind of the downvoter. Unfortunately, the technology to detect that isn't available at the moment. What LW software can detect is that user X downvoted N1 comments by user Y on day 1, N2 comments on day 2, etc. As long as N is "a few", I would be wary of drawing "mass-downvoting" conclusions from this pattern.
Also, I would recommend not getting into a technological arms race with people want to game the karma system.
Related article: Polyhacking
Note: This article was posted earlier for less than a day but accidentally deleted.
Although polyamory isn't one of the "official" topics of LW interest (human cognition, AI, probability, etc...), this is the only community I'm part of where I expect a sufficiently high number of members to have experience with it to give useful feedback.
If you go looking for advice or articles about polyamory on the internet, you mostly get stuff written by polyamorists that are happy with their decisions. Is this selection bias? Where are the people whose relationships (or social lives, out anything) got damaged or ruined by experimenting with Consensual Non-Monogamy?
I'm posting this hoping for feedback, negative AND positive, on experiences with polyamory. I considered putting this in an Open Thread, but it occurred to me that many other LW readers might be interested in whether polyamory has drawbacks they need to be aware of. If you have experience with CNM (including first-hand witnessing, which has the added bonus of not requiring you to out yourself while still participating in the dialogue), please comment with your overall impression and as much detail as you would like to include (I am also putting my experiences there rather than in this post). If you've seen multiple poly relationships, multiple comments would make tallying slightly easier. I will try to upvote people who feed me data, a la LW surveys. If there are sufficient comments, I will periodically go through them and post a rough ratio of good to bad experiences at the bottom of this article.
PSA: The Username account is available for use by any who wish to remain anonymous. The password is left as an exercise for the reader. Hat tip... Username.