So here's an example of how Linkedin can be useful. Rebecca, the Tokyo bureau chief of CNN had emailed me asking for information on the moblog conference because she was interested in possibly covering it. I had been meaning to get around to introducing her to Adam. Then I received a Linkedin request from Adam asking to be introduced to Rebecca to see if she wanted to cover the conference. I clicked, typed something like "you guys should talk" and... done. It was a very easy way for me to add value and I ended up helping to friends without taking much of my time.
I've been getting a steady flow of requests now and about half of them are just tests, but I really do think that Linkedin will help me manage requests for introduction. I get SO many of them via normal email and many fall through the cracks. Intros are such an easy way to help people and add value, but they are really a pain to keep track of. It's usually just a matter of searching through my email to find the email address of the person that needs to be contacted, but often I'm too busy to do that. Linkedin solves that problem. It also forces the introducee to write something focused, rather than, "I wonder if you might be able to introduce me to..."
UPDATE: Discussion has moved to the wiki