There is only one kind of comment I actively dislike, and that is unrequested advice. Please, never say "you should do ___" because it will make me feel disrespected, like you think that you can make better choices for me than I can. Feel free to tell me about similar experiences, but don't assume that I haven't already tried the thing you're thinking of. Also, if I ever give you unrequested advice, feel free to tell me off about it -- I won't get defensive, I'll just apologize and try to do better. I try not to give unrequested advice, but sometimes I yield to the impulse! which is why I understand when others do it, even though I don't like it.
On other people's posts, I tend to comment only if I have something to say, so if all I can think of is "I see" or "I agree" or "huh, interesting" then I probably won't comment. But I do read, carefully. On comments on my journal, I always INTEND to comment back but it tends to not happen in any kind of timely manner, and once it's old enough I don't do it at all. I want to get better at this because some of the comments I REALLY want to respond to. I need to let myself skip some comments instead of being fixated on doing them in order. I very much read and appreciate your responses though!
LJ is asking for feedback about a potential 'like'ing system. My response: people who have something to say will still comment. This allows people to show that they read it even if they don't have anything meaningful to add. I would much appreciate this and I think my friends list would too. and I think you should call it a "nod." That's the emotional feel of it.
I would love to get 'nods' on my post to let me know who read it and appreciated it. LOVE LOVE. I used to have a tracker that I could sorta kinda use that way but this would be much more accurate. If you agree please go over there and add your voice -- they put this post up YESTERDAY but the first commenters were negative so they're scrapping the idea, wtf.
(there is also a place to give feedback on the site redesign -- which they are planning on forcing! switching back is only because it is in beta! please tell them NO.)