Social networking is not just about who you know. It's much more about who they know. My good friend Jan Vermeiren points out in his excellent book "How to Really use Linkedin" that it's your second level contacts who can really help you. When you have a mutual, trusted friend in common, it is often very easy to effect an introduction. And assuming an average of just 200 first-level contacts, your second-level contacts will number 40,000, which is a large pool of potential business partners, employers or clients.
It's the same on Twitter, although the numbers are even larger. For example, I have around 2,500 followers. Assuming an average of 500 followers for each of them, I can reach over a million people in two steps. It's this, in my opinion, that is making Twitter the "collective brain" of the planet. Once, I used to turn to Google if I had a question I couldn't answer. Now I turn to Twitter. In the last week alone, It has helped me find the source of an obscure quote, located a cosy bed and breakfast in Sedona, Arizona, and allowed me to set up an interview with an innovative PR company. All of the responses came back within ten minutes.
It's not who you know, it's who they know (and what they know, too).