Now this is what the Web is all about.
If you don't know Technorati, you should. It is basically a blog reference index that can be used to see who's saying what in the blogosphere. For isntance, if you want to find all of the blog posts about the Huygens probe landing on Titan, you might search for Huygens. It's updated in pretty close to real time, so you get a good feel for what's happening.
Now things have gotten even better with tags. The idea is that a blogger "tags" each post with category keywords telling what the post is about. So again, I might search for Huygens, but this time, what comes up are the blog posts tagged with that word, meaning they are primarily about Huygens and don't just mention it in passing. As a concrete example, this post will come up in a general Technorati search for "Huygens" (or a Google search in a few days), but will not come up in a Technorati tag search. It will, however, come up in a Technorati tag search for "Technorati" or "tags," because that's what I've tagged it with below (and incidentally, you can click on the tags to search for them).
Those of you who know and love the photo-sharing site Flickr will be familiar with tags, because searching for tagged photos is one of the best things about that service. As a bonus, Technorati searches and displays Flickr tags simultaneously, so you really get the whole zeitgeist.