I am on LinkedIn, and I don't actively use it. The only active user I met once was a recruiter of creatives. She logged into LinkedIn and we saw her private inbox. Filled with hundreds of messages about people in her industry who were looking for someone or looking to hire someone. I was amazed, we were amazed (this was 2006). She gave us one really good tip - almost all the job postings on LinkedIn are posted with the name of the hiring manager. That is why job searching on LinkedIn is better (even if they aren't posting the hiring managers' name now in 2011).
At a bar a month ago, I met someone who asked if I knew a friend of his who used to work for my company. Quick search of the LinkedIn app and found him. LinkedIn is gold for finding out where someone in the technology industry is now working. Especially if you have connections who have hundreds of connections.