Having been on both sides of a flash downvote (guilty!), I can tell you that these vendettas are not very effective on a forum of this size. Enough people read old comments and tend to upvote comments they otherwise wouldn't if they feel it's unfairly penalized, even if the comment is old. It's a lot more effective to post a quality reply which convinces other readers that the comment in question deserves a downvote.
Hmmm. It's true that one of the cases where I'm most likely to upvote is where I see a comment that looks fine to me that has a negative point total. But flash downvoting won't necessarily produce any negative point totals, and I'm a lot less likely to spring into action for a post that merely doesn't have quite as many positive points as it should (since I rarely have a very firm idea of how many positive points anything should have). Then again, perhaps in cases where nothing actually goes negative, not much harm is really being done anyway. So I may...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.