If you're crazy about blogs, Technorati is the way to go. It organizes blogs by broad topics and you can also search for items within the blogs.
I think tagging is an inevitable result of regular users sharing their information globally. Many may welcome tags as a "common sense" approach to searching. Others may be frustrated because "common sense" is, after all, not universal. And there is also the confusion that can result from not having an authoritative tag for something like "pool", which could signify a swimming pool or the billiards game. I think tags are a great way to find something informally, especially if you're navigating in a context that's familiar.
Technorati could be used as a way to introduce students to blogs. They could follow one they find interesting and keep a journal on it in preparation for writing their own.