Sphinx is gaining popularity day by day and many high traffic websites are migrating their search engines to Sphinx. A few who have already done this are listed next (Ref: http://sphinxsearch.com/info/powered/):
http://craigslist.org/: Craigslist is one of the world's most popular and highly visited websites. Thousands of people search the classifieds on craigslist every hour. They moved to using Sphinx in November 2008. Craigslist is known to have the busiest Sphinx server in the world.
http://www.joomla.org/: Sphinx is used to improve search through their forum, which comprises more than 700,000 posts.
http://mininova.org/: One of the biggest sites to search for torrents. Sphinx on this site servers more than five million searches per day.
http://boardreader.com/: The website with the biggest Sphinx installation in terms of data. It is indexing over two billion documents now.
http://netlog.com/: This is a huge social networking site with over 35 million...