If you are serious about Drupal search, then you are probably aware of the fantastic integration between Drupal and Apache Solr - the open source search server based on the Apache Lucene search library. The Apache Solr Integration module offers some very straightforward instructions on replacing the core Drupal search with Apache Solr (the same search server that powers drupal.org and www.whitehouse.gov).  And in replacing core search, the Apache Solr Integration module devlivers pretty much exactly what you would want and expect, such as:

1. Faceted search
2. Replacing taxonomy pages with Solr search
3. Result biasing
4. Content biasing and exclusion
5. The list goes on and on...

But what happens when your requirements are a bit more complicated than just replacing core search?