I think the LinkedIn is pretty awesome. Most people I've talked to have had a mixed experience with it so far, but I think with the addition of Groups and with their excellent work with Jobs, they're really valuable.
Luckily, they are making things happen for students looking for jobs.
Elizabeth Reaves at LinkedIn writes:
LinkedIn has a resource for college grads and is offering a free premium account for users who go through the three steps listed in the grad guide (to get to a 80% complete profile): http://grads.linkedin.com/
From personal experience looking for a job in start-ups two years ago, LinkedIn can be a great resource for finding interesting companies, finding "ins" at start-ups, and vetting opportunities and offers.