A friend recently invited me to join his network at LInkedIn. It seemed like a cool thing, so I invited a bunch of people to join my network, only to find out that many of them were already signed up. Who knew?
From their "About" page: "When you join, you create a profile that summarizes your professional accomplishments. Your profile helps you find and be found by former colleagues, clients, and partners. You can add more connections by inviting trusted contacts to join LinkedIn and connect to you."
My profile is here. I'm always looking for interesting contacts, connections, and business opportunities.