Instead of playing catchup - go for the home run
Sully Sullivan commented
There are some great FOSS enterprise search solutions, and especially those from Apache (Apache Lucene, Apache Nutch, Apache Solr) and proprietary from Microsoft (Search Server 2010 Express, FAST for Sharepoint Search) would be good for inclusion. It would help with directory sites, eccommerce, and sites where a lot of content is closely related and a search term isn't enough or will always be too vague to narrow your selection.
Steve Amerige commented
Faceted search (http://en.wikipedia.org/wiki/Faceted_search) is a key search feature for websites that have a lot of content. This is useful not just for e-commerce, but also for directory services, API browsers, and for websites where taxonomies are important. This feature closely aligns with having a CCK (content construction kit) and is so important.