Facebook…linked in…career services

Thankfully I have already received an internship for the summer but over the past few weeks I have been receiving a large amount of emails and other information about the various ways to network.  Our society as a whole is constantly being pounded with more and more information.  This may seem bad but it is definitely helpful in certain circumstances…such as networking for a job.  My question to any of you bloggers is this — Which social networking tool is most effective to network for a potential career?