Solr is something you can implement faceted search
with, but I'm not sure what you'd want from emacs integration...
Faceted search typically helps you drill down to find a set of objects or other discrete entities; not really for searching within such an entity.
In other words you need to have a set of objects/entities that are already fairly well-structured or have reasonably coherent attributes on them from which to build the facets.
In the worst-case, a faceted search view of your computer's filesystem might only be able to show you facets based on datetimes (created/modified), filesize, filename extension, permissions etc. but nothing about the content of the files.
If you've drilled down to a collection of .mp3 files, your faceted search engine might then be able to offer facets based on MP3 tag data.
A good example is RS Components and Digi-Key. I can't pull one up now, but sometimes I find that these suppliers won't show you many facets until you've drilled down into a subset of their product range that has a common set of attributes - at which point you can suddenly filter by current rating, voltage, MTBF, etc. whereas at some broader category view you might only have brand-name, stock status and lead-time facets.
See down the left bar here: http://au.rs-online.com/web/c/semiconductors/processors-micr...