Eurekster
Eurekster: a social search engine.
From the material on the web site, eurekster lets members set up social networks friendster-style (though without all that personal info stuff). as you search the internet, eurekster observes which links you follow. then when your friends do similar searches, eurekster promotes links in their results that you clicked on. and vice-versa of course. The result, presumably, is a sort of community-determined idea of what links are good.
Can this work? It seems relatively rare that I'll be searching for something my friends have been searching for (except in the case of memes-of-the-moment). On the other hand, being friends perhaps we are more likely to search for the same things. And if eurekster got sufficiently large (e.g., I have something like 1.4M people in my friendster network), it could start to work. On the other hand, do I really trust the opinions of 1.4M people who are 4 hops from me more than, say, google's pagerank? not sure.