Found on Facebook: Search returns on Cuil can include hits from the searcher’s Facebook network, shown on the right-hand side of the screen, if the user opts in.

Cuil launched in the summer of 2008 amid hype that it was a “Google-killer” because it claimed to hold the largest search index in the world. But after it launched, servers crashed and algorithms sometimes gave irrelevant results. But the company hopes the social-search strategy can bring it back.

Cuil’s new effort is, of course, hardly the only social search effort in the business. Facebook and other social-networking sites already let users search within their networks, albeit with sometimes-spotty results. And Worio offers a Facebook application that generates recommended Web links, akin to search results, based on analyses of information from a user’s social network. (If you were searching about asthma or Ecuador, they might offer websites offering medical advice or travel tips.)

And in October, Google announced, within its Google Labs test bed, a technology called Social Search. This allows users to find results from their social networks; but only those results that are already publicly available on the Web, such as websites, blogs, status updates, and other public content. The Google technology identifies your social network based on your Gmail chat buddies, the blogs and other websites you link to, and by indexing publicly available content from services including Twitter and FriendFeed.

But in the case of Facebook, the technology would only find the same public profile pages that are already visible and can be found with general Web searches. Google has not disclosed any formal launch plan for its social search efforts.