There is a subtle yet profound difference between blogs and previous methods of communicating on the net. Blogs are anchored to a location, which requires ownership. This difference is the major factor which lead to it's current popularity. Unlike email, you can't forge entries from a blog. This allows trusted relationships.
When you read a blog for the first time, you're deciding if you like the author or not. This uses our natural instincts for deciding who we want to build relationships with. It grows over time. You'll develop a set of favorites that you read over time.
When someone makes their list of favorites available, it's a blogroll. When you put someone on your blogroll, it's more than just a person reference, it becomes an endorsement. This means that people think twice before adding someone to a blogroll... which helps keep the quality up.
Blogrolls and easier tools made blogging popular. This lead to the current rush of traffic. All because of the ownership and identity and relationships inherent in the simple fact of a URL anchor.
The tools make it dead easy to link to other blogs, and build the live web. This means that the sheer amount of stuff to discover will probably continue to grow for quite some time. However, this presents the problem of data overload.
The solution that Doc Searls uses is to "aggressively subscribe to RSS searches". I see a danger in that because it breaks the mold of relationships that got us here.
When we were strictly manually building blogrolls, any spam blogs (splogs) that arose would quickly be discounted, and just not added to the growing web of links. This is the only form of spam defense which isn't likely to be overwhelmed in the near future. It's pretty much 100% effective.
When you rely on a search engine to find things for you, you're making a tradeoff. You're taking input from a far larger range of sources, but you loose the inherent filtering present from relationships. This is where the opening comes for spam blogs.
We can either shun search engines, or possibly find ways to make the relationships more explicit so then can be machine readable. If the search engine could factor in your web of trusted relationships, it could then help you manage a much larger group of "friends", or more appropriately non-spammmers.
It remains to be seen if this is a good idea or not. I've revised this since it's original post, I hope this is a lot clearer.