The Technorati Blog Directory had much more relevance when blogging first became popular. There was a time where if you were a blogger who was even half-way serious about getting your message out into the blogosphere, you made sure you were listed in Technorati. In fact, many bloggers were down right obsessive about scoring high authority rankings with Technorati.
Authority rankings were seen by many bloggers as the ticket to being read and respected by many. Getting listed in Technorati's list of the top 100 blogs was the ultimate honor. These days, however, Technorati no longer carries anywhere near this importance. Relative to other blog directories though, it is still one of the big boys, perhaps the biggest of all. Plus, it is still hands down the largest database of blogs and blog posts on the internet.
Being listed in Technorati also used to count more when it came to garnering high Google search engine rankings. It was thought that your authority score mattered here too, although that was never verified in any scientific way to my knowledge. Mostly it was a legend that was almost whispered about on various internet marketing forums.
What is definitely true now is that a Technorati listing does not mean as much today in terms of your Google search engine rankings. Getting listed in the Technorati Blog Directory would certainly not hurt your ranking but you shouldn't expect a big boost in rankings after your blog gets listed either.
Some blogs seem to land in the Technorati Blog Directory without being manually submitted for consideration. However, most bloggers do find they have to go through the registration process and then the more complicated process of "claiming" their blog for their blog to be listed. This involves filing out a form and then taking the Technorati code that is emailed to you and placing it in a new post on your website. This is supposed to get Technorati to list your blog and also index your posts.
What many bloggers don't realize is that you can lose this indexing if you fail to post for a period of longer than 30 days. This even applies to otherwise active blogs that simply take a temporary hiatus due to vacation, illness, a big job assignment, blog burn out, etc. Therefore, if you think you are listed and you are being indexed, you may want to verify this is still happening if you have ever had a period where you didn't post anything to your blog for a while.
I do like the fact that you can achieve an authority ranking in more than one category since many blogs can easily fall into more than one category. Authority scores these days seem to be based on relevancy to the category, frequency of new content, and how many times other blogs are linking to your blog.
I also do occasionally like to use the Technorati search engine that searches recent blog posts on active blogs to see what is being discussed the most on certain topics I am interested in. However, this is probably fairly unusual as I do not believe many people use Technorati anymore in this manner.
Although blog directories in general no longer carry the same relevance they once did, they are still important enough that bloggers should make sure their blogs are listed in at least the top blog directories.