While helping maintain the New World Encyclopedia, I tried to install the LuceneSearch extension to replace the default MySQL-full-text-based search used by MediaWiki. Since our server did not come with any pre-requisites necessary for compiling and running Java applications, I spent quite some time on it, and still did not get it to work.
All of sudden (hint, hint,) a message came to the mediawiki developers list about a new search extension that uses Sphinx search engine. Installing Sphinx was a breeze! The extension was an initial “request-for-comments” version, so I started working with the author to spruce it up. You can see the results at NWE, MediaWiki.org, and SourceForge.