Metcalfe's Law postulates that the value of a network increases proportionally with the square of the number of people in the network. Skeptics argue that the value increases less rapidly - n*log(n) seems more reasonable by the time you factor in distractions from the network size (think spam).
In any case, many of the hottest products on the market today, like the free phone service Skype and others, derive their popularity from Metcalfe's law. In fact, you can trace the success of the telephone, fax machine, email, and instant messaging all to forces unleashed by Metcalfe's Law.
Smart recruiters know the law applies to the recruiting business as well. They know that the more they expand their world of candidates and contacts, the more business they get. You can't force a piece of business to close, but you can build up a pipeline through networking that makes it inevitable that a lot of business will close.
A recruiter acquaintance in Alabama, a solo-practice guy, is taking this to the next level. A while back, he added blogging to his quiver of networking tools. At first, the blog just drew in his recruiting peers - and slowly at that. But with time, he caught a break or two and got some media coverage (the press loves stories about jobs). He's starting to get traction in the form of speaking engagements and luncheons with the HR community.
He's already a successful recruiter, but now he's able to leverage his time like never before.