Thing #4 (I know out of order, again)

By commenting on other peoples blog you in a sense having a conversation with not just that person but each person that has commented on that blog.  It creates a community because it can take people from all over the country and turn them into a online community interested in the same things.  I agree that comments should be meaningful and not just one or two words.  If you just post a few words the blogs author might not know how to respond to that and it will not help further the conversations going on between other people on the blog.  I also think that comments are important because it will keep the blogger going.