Many people worry about filtering information in their feeds, leveraging searches and watches for specific terms. To me, though, the feeds are the filters. One of the best things about RSS/Atom is finding people who you trust to filter the vast amount of information available on a particular subject area for you.
For instance, Jack Vinson serves as my KM filter. While KM is among the topics I follow, it's not something that I can spend much time on. Before I met Jack at CSCW, started reading his blog and finding value there, my KM research was haphazard at best. Now I get a steady stream of relevant KM information. The blog/KM intersection that Jack occasionally writes about is of particular interest to me.
Russ Beattie is my mobile filter, but it is a completely different sort of "relationship." I spend less time on the mobile space then I do on KM. I've never met Russ, and we tend to disagree on lots of things - AJAX, the relevance of screen size, the usefulness of a quarter VGA screen, etc. He's responded (with vitriol) to comments I've made on his blog, but he wouldn't recognize my name or this site. However, his extreme passion for the mobile space, his personality, and the fact that we often disagree makes him a good filter for me in this space.
On the other hand, I read scads of blogs about collaboration-related topics. This is where I serve as a filter for others -- not just via the blogosphere, but in my role as an IT architect. What's important isn't just what's going on in the world at large, but how it affects or could affect our company. Similarly, I read Bruce Schneier and the endlessly revolving InfoWorld security columnist, but I rely heavily on Guy and his coworkers for analysis of what's happening in IT security.