What if everyone posted a similar contentless "thanks" post on every article they found interesting? Such posts would dominate the comments. There's already a "thanks, this is very helpful button" -- it's called the up arrow.

EDIT: I'm not trying to troll here, I'm serious -- do you think comments like this add something to a discussion?

Experience shows they're harmless.

New users are explicitly told such comments are ok: http://ycombinator.com/newswelcome.html

If everyone would do that, then that would be a problem. However, not everyone is doing it and it doesn't seem like more people are starting to do it. It's just not necessary to downvote superfluous comments; not getting any upvotes is enough of a signal.

You could just upvote the "thanks, this is very helpful" comment...

Guilty as charged, let me explain why. When this was posted first, it looked like a pattern I've seen before on HN, some spammer posts a link and then uses a sockpuppet (or more) make it seem as though the content is great.

For another example of that see here:

http://news.ycombinator.com/item?id=941568

So I was a bit quick on the trigger there. On the other hand, if I would have been able to undo my vote (reddit style) I would have done so.

edit: it seems quite arbitrary to single these out for being modded down, there are much better examples of good contributions that got dumped on.

You can tell they're not sockpuppets by the account ages. In the situations you're talking about, the accounts are mostly new.

In this case, yes, but I only clued in to that later.

The link I posted above I would say is definitely a spammer+sock puppet or at least an acquaintance of a spammer.

I've been noticing many acceptable comments being downvoted a lot recently.

A five-word upvote is not an acceptable comment.

I down-voted it for poor punctuation.