Ann Althouse delivers a good summary on the topic of comments on blogs, which, since I just enabled comments on this blog, is of some interest to me.
Perhaps someone has mentioned this before, but I think there are two kinds of blogs that transcend the left vs. right divide. Some blogs, like Instapundit, exist primarily as clearing house for links and a quick description of current events, mostly of a political nature. Other blogs, like mine, exist primarily as an outlet for my rage, joy, ideas, and analysis (i.e., commentary on a variety of things). For the former, since the point is to direct people elsewhere, comments make no sense. For the latter, it seems to me that they do make sense if one is interested in what others might have to contribute–including corrections or refutations.
Of course, there are lots of blogs that do both, probably the majority. In that case, it makes sense to me that if the point of your post is only to direct people elsewhere, you disable comments for that post, and if the point of your post is to delve into some topic in more depth, you enable them.