Having entered the blogging world just about a year ago, I had never heard of Technorati. After playing with it for a little while, I can see where it can be useful. If you have a really great website you want to get out there then you can register it with them. I also liked that they had a lists of the most popular tags out there.
One thing that I did not like is that you have to register your blog for it to come up, but at the same time that will keep a lot of the nonessential blogs off of the site.
I love reading reviews of books, so I typed in Young "Adult Literature Reviews" and was able to find a lot of cool sites for reviews. This is a site I will use and commend to people who enjoy following blogs!