I had lunch yesterday with Flemming Madsen, who runs a successful business helping organisations figure out who is influential online. You tell Flemming what issues concern you, he'll try to figure out who the key influencers are. What he does is to add a layer of analysis above the standard tools which measure popularity. That's significant because authority is rather different from popularity. For some subjects, you might find BoingBoing has the most linked posts, but that doesn't mean their voice is the most influential. I'm going to take a test drive of Flemming's systems in a couple of weeks and I'll keep you posted.