Dave Winer:

I was going to point to the Technorati feature called Tags, but the docs made me uncomfortable. Who cares if they're friends with Flickr, Delicious, Typepad, etc. What does it mean for two products to be friends anyway? What happened to open protocols and level playing fields? ... We don't care if you're "friends" with other products, just tell us how you support open protocols and we'll figure out how to plug you in.

Technorati's tag support doc:

If your blog software supports categories and RSS/Atom (like Movable Type, WordPress, TypePad, Blogware, Radio), just use the included category system and make sure you're publishing RSS/Atom and we'll automatically include your posts! Your categories will be read as tags.

I was going to write a guide to how to publish MT entries with keywords as categories in your Atom feed so they work with Technorati Tags, but you can't iterate space-delimited keywords without a plugin. Technorati's docs also don't say if they're using Atom 0.3 dc:subject or Atom 0.4 atom:category.