Categorizing posts with keywords is not new. There are solutions which create a new column for your blog, where you can define categories.
My Webpart will look in your posts for Technorati links. Many posts are tagged with Technorati links, so that you can look for a tag, and find posts on many blogs for this tag.
You can create Technorati links with the Live Writer, if you want to blog with it.
How does it work?
The Webpart will look for links <a href=“technorati.com/tag/ and generate a Tag Cloud from the links. If you have other links which you would like to use for Tags, you can configure the link in the Webpart properties.
Selecting a Tag from the Webpart by clicking on it, will show all related posts. This way you can navigate within your blog posts by selecting Tags and not going through the Technorati page, if you use a Tag Cloud generated by them.
The Webpart uses a SPQuery to find all posts with the link in it, groups them and generates the Tag Cloud. A click on a Tag will bring up a list with all related posts.
For performance reasons, the Webpart caches tags for 5 minutes. With the Refresh Button at the bottom of the Tag Cloud you can force a reload of all tags.