For those of you who missed Marti Hearst's talk on faceted search interfaces last week, here's a powerpoint with most of the same content. The first twenty or so slides provide a nice, very approachable primer on faceted searching:
http://flamenco.berkeley.edu/talks/chi_course06_4_23.ppt
There's lots of other good material in this presentation, including tips on designing and evaluating faceted interfaces. Also included are the results of some user testing that Hearst and her colleagues did on a fine arts site, where their faceted interface handily beat a Google style interface.
Naun.