If I'm going to post comments, I always make sure it is relevant to the topic, plus I redirect to a site that is also relevant. Eg, I have a blog about music, I'm not gonna post on a travel blog with my music site link. I try to make sure the comment adds value to the discussion or topic. But I see what you mean, where you get 200 posts of just link. And that is nasty indeed. So IMO, it is good to post comments, but make sure they always have a relevancy to the subject or discussion you are going to comment on.