I don't know the definitive answer, and perhaps I'm not correct, but here are some thoughts I've had on the subject.
If you comment on the work of people you are following, I think it helps your score.
If you go Hub Hopping, make comments on new writing, vote up or down or flag bad hubs that it helps HubPages, and this might have some effect on our commenter score.
Very short comments like "great hub" or "I like it!" are not really helpful to anyone.
I think that detailed comments are only helpful if they reference the author's hub, not if they are used to relate a long personal experience. (Although that may be interesting!)
Does it help to share other people's work? I suspect that it might.
Putting a link in your comment will make it look like spam.
Take the above for what it's worth. I like to read and comment on other hubs, but in the grand scheme of things, I'm not sure how much our commenter score really matters.