LinkedIn is a service designed to help you find contacts, recruits etc. You can invite people you know to be part of your ‘network’ of referrers, and you can then search for people based on particular criteria. It’ll tell you how many degrees of separation there are between you. You can only actually make contact with the people if those in the chain between you agree to forward your request. When the system gets past beta, you may need to make a small payment to LinkedIn as well.
This has been an obvious potential use of the Net ever since the whole ‘Six Degrees of Separation’ thing – see the Columbia SmallWorld project, for example, but this is an intriguing commercial implementation of the concept.