I am planning to catalog the major tools and social networks available to the masses, and today I begin with LinkedIn, a service that I use myself...
Taken from The Urbach Letter:
Considered by many to be the premier business networking service, LinkedIn has about 50,000 current members as of this writing. In November, it received a $4.7 million investment from Sequoia Capital (the venture capital firm behind Google, Yahoo, and PayPal). What do they expect to get for their money? There's great expectation that LinkedIn will become an essential part of the upper-echelon business culture. The service is geared to C-level executives, investors, influential managers, and other hard-to-reach people concerned about building contacts with others while tightly controlling access to themselves. LinkedIn exists solely as a service for people who want to receive "warm" introductions to other people. There are no discussion forums, event listings, or the extra content you'll find in other services. But it has an excellent access system. The names and profiles of other people up to four degrees of separation away are visible to you, but you can't get contact information unless it's explicitly given to you by the target person. Before it even reaches your target, every link in the chain must approve your introductory request. Like a firing squad, where each gunman aims at the victim's heart, but one gun contains a blank round, this system allows a person in the contact chain to break it anonymously, with a relatively clear conscience.
This strictly enforced chain of trust ensures that when connections are made, they're well-placed. The anonymous black ball turn-downs prevent "dilution" of the list by reducing the tendency to admit marginal players. However, it also means you won't necessarily grow your network as quickly as you can elsewhere. You'll need to receive an invitation, or be proactive in getting your top-shelf offline contacts to sign up. There's a bit of a Catch 22 here. To build a network, it helps if you've already got one to share. Again, human nature at work. If you want to get, you've got to give. Both parties must believe there's something to gain.
LinkedIn allows you to upload your address book (Outlook and others) to check which of your existing contacts are already on the service. It also facilitates emailing your non-member contacts invitations to join the service. Both of these features are important for jumpstarting your network.
By the way, LinkedIn has become a preferred source for journalists to make contacts with people who are authoritative and trustworthy.