I don't know too many people who have had success with LinkedIn from an Internet marketing / traffic perspective. I think it's best for job recruiting and networking. Of course, that's not to say people aren't using it for Internet marketing. I just don't think it's as common as Facebook, Twitter, etc. when it comes to social networking.
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your average Joe wouldn't know what that is. I know of it but I never actually checked it out. I think you should stick with the top social networks Lisa just mentioned.
Lisa hit the nail on the head. It seems more for recruiters. Plus ppl aren't too willing just to accept your request to be linked together. From what I hear, from Linkedin Lions, it's all about who is in your linkedin who makes you you on there.