If I was a web search company, I'd allow users to upvote or downvote their search results (this would increase or decrease their prominence on subsequent searches). This could be done on a per-site, or per-page basis.<p>Then I'd use one person's preferences to alter how other people receive search results (on an optional basis; if people didn't want their results filtered like this, they wouldn't have to.)<p>But I wouldn't just use an average of all users; it'd be too easy for spammers to create fake accounts to upvote spam. No, a user's search results would only be affected by what their friends upvote and downvote (or possibly their friends of friends as well).<p>This would make it in a user's interests to link to their friends and have their friends rate websites, as everyone uses web search. So people would want to promote the search engine to their friends.<p>To give people more of an incentive to proselytise the search engine, I'd add social features such as a twitter-like service (allowing public, friends-only, and named-recipients-only messages), chat (text, voice and video-voice), an extended-length messaging service (you could call it, I don't know, a "blog" or something) that also allows pictures, and RSS feeds of one's own and one's friends' public entries.<p>I'd also add a "fan" feature (intransitive, as opposed to friendship which is transitive). People could create lists rating websites, and others could fan those lists.<p>Maybe someone like DuckDuckGo might want to implement something like this?<p>(Incidentally, DDG market themselves as being privacy-friendly, which coupled with the recent subpoena of Wikileaks' Twitter data, suggests there may be an opportunity for a competitor to Twitter that is more privacy-minded).