An alpha version of Wikia's open source Wikia Search has gone public, but the consensus seems to be that this user-tuned search engine has a long way to go to compete with the likes of Google.
Read more about it at "Jimmy Wales Argues That His Wikia Needs More Time," "Wiki Citizens Taking on a New Area: Searching," "Wikia Launching Human-Powered Search," "Wikia Search Alpha Preview Leaves Much to Be Desired," "Wikia Search Is A Complete Letdown," and"Wikia Search—Miles Behind the Competition."
