Search Patterns' excerpt on faceted navigation is online

Peter Morville & Jeffery Callender wrote in their book, Search Patterns, that
"Faceted navigation may be the most significant search innovation of the past decade."

We see it mainly in e-commerce, but it can help in many other situations.

Chapter 4 of the book is available at AListApart - Design Patterns: Faceted Navigation

"Faceted navigation addresses the universal need to narrow. Consequently, this pattern has become nearly ubiquitous in e-commerce, given the availability of structured metadata and the clear business value of improving product findability. Faceted navigation is being deployed rapidly across an impressively wide variety of contexts and platforms. In the world of search, faceted navigation is everywhere. "