What makes me laugh the most these days are people who claim to know how to make anything go viral and therefore influence a critical number of people to adopt an idea.
Granted that there are a lot of persuasive and brilliantly executed stuff on the internet, there hardly exists a foolproof way of putting an accurate metric that would show just how influential one is.
Visit counters, Alexa Ranking, Technocrati Authority, PageRank, the number of people in one's "community", how many votes you get for one contest or another, and other such measures are mere ego-candy. The fact is, any of these "influence" indicators can be "gamed", but that is not to say that these indicators are completely worthless.
I guess, the only proof of influence or how influential one is can be judged best by the effect you have on a population.