You can now power your vanilla forum with Sphinx! Sphinx is an open source full text search server, designed from the ground up with performance, relevance (aka search quality). Sphinx indexes up to 10-15 MB of text per second per single CPU core, that is 60+ MB/sec per server (on a dedicated indexing machine). This is the same engine that Craigslist uses to power their site which sees 50+ Million queries each day.
Please see the github README for all information regarding requirements, features, installation,changelog, etc.
Live Demo from Roberts Space Industries that serves hundreds of thousands of visits
Info about sphinx: http://sphinxsearch.com/about/sphinx/