There are obviously lots of reasons to read blogs.
You like the blog editor's point of view and want to hear more. You completely disagree with the blog editor's point of view and want to hear more. You like the subject matter, the candidate, the sports team, etc. You care about the issue or cause. You have the opportunity to share your voice and read what others are thinking. A particular blog might combine interests - sociology and sports, history and food, whatever.
My blog, Senate 2008 Guru: Following the Races, for instance, has a very specific scope. If you are interested in the 2008 Senate races, this is a blog for you. If the Senate races and Senate candidates aren't remotely interesting to you, but you love French cuisine or the Seattle Mariners or model airplane building, it's maybe not the blog for you.
Please share your comments - why do you read the blogs your read? What makes them appealing to you? Beyond solely reading news and opinions and posting comments, are there features you look for? What keeps you coming back for more?