mavens and The Tipping Point

There's a great quote from Malcolm Gladwell's The Tipping Point that just has my mind reeling. I can only paraphrase it right now: in an age of information overload, we rely on word of mouth to deal with complexity. The word of mouth we rely on, this primitive communication, all comes from specialists in our network. These specialists, who Gladwell calls mavens, can provide the best kind of product referrals, distilled information, and advice because they're simply obsessed with data in one or more niches. He says that it's a certain kind of person--but I'm inclined to believe we're all vessels of trivia in some category or another. This becomes important when we think about how to promote learning / competency / agile skills / decision making / etc. If we could use a networking tool and nominate our friends as mavens on one category or another, we might benefit better from our networks... is there something that already does this?