Joe Bork captures an important property of weblogs:

These are all fairly superficial reasons, however. Public folders and newsgroups and mailing lists all deal with a single topic of discussion and many people. A blog has a strong relationship with a single person and many topics of discussion.

I've mentioned this before, but one of the attractions to reading (or writing) a blog is that it has a voice -- that of the author. I might read Bugtraq because I'm interested in what people have to say about security vulnerabilities in general, but I read defective yeti because I'm interested in what Matthew has to say about, say, historical biographies and scooters specifically.

If you are interested in topics, the best way to find out is to find the thought leaders for that topic. Blogs can help identify who the thought leaders are and give them a voice. It frequently happens that people who are thought leaders are thought leaders in multiple domains, so blogs help cross connect domains by focusing on people. I tend to navigate blogspace in two dimensions. I have lots of interests, and want to find out about the latest and greatest. So I watch blogs for topics that interest me. When I do this, I'm navigation by topic. Inside a topic I navigate by people, which frequently leads to cross connections, and a new topic to navigate on.