Apart from their own site many companies have a profile on LinkedIn to show just the essentials of what they do and who they are, just like your personal profile is supposed to do. That's one way to use LinkedIn as a source to find a job or assignment as a partner, getting a contract etcetera. The reversed method is to find a company's website without the chance to make a typo in the URL or the company's name in your favorite search engine. Besides you see eventually 1st, 2nd, 3rd contacts who work there, a reference in the blink of an eye.

LinkedIn has a lot of positive characteristics especially if you dare to compare it with FB, MySpace and a couple of other, less famous sites.

Specialized job seeker/recruiter sites are valuable as well. Applying by just one to three mouse clicks and typing few bytes are valuable as well. I use some of them to get a better chance.