When I typed in "LinkedIn success stories," I found they actually existed. Nineteen whole search pages worth. Judging by the personal accounts that came up, LinkedIn seemed to be a useful tool for those already in the work force rather than those looking for entry-level positions. This obviously makes sense because they know more people. The more people you know, the better your chance for networking. I.e. The better your chance of finding a job.
One example of a success story was David T. Stevens, who after losing his job at a radio station, immediately changed his LinkedIn status to "I'm up for grabs, who wants me?" Within a week he had a new job as a program and event's manager.
However, in all of these accounts, the idea of "branding yourself" was the most important aspect. It could never hurt to do this too early, even if your credentials and network circle aren't as stellar as you'd like them to be.
Anyway, see the following blog for 10 Ways Journalists Can Use LinkedIn:
Also, if you are graduating and looking for entry-level positions see this link: http://www.onedayonejob.com/
Happy job hunting!