I've been trying to figure out how to utilize profesisonal networking sites such as LinkedIn and Soflow for a couple of years now. Professional networking websites pre-date MySpace but are only now being looked at as a serious source of clients and partners.
Guy Kawasaki has wirtten an article
Ten Ways to Use LinkedIn that's got some interesting facts about people with a LinkedIn profile page such as "People with more than 20 connections are 34 times more likely to be approached with a job opportunity than people with less than 5." He also describes some great potential uses of it such as gauging the helth of a company or industry.