It is a great way for individuals to stay contacted professionally to others of similar interests. It is much more than a place to post your resume to find a job. It has kind of redefined the meaning of your resume because it causes you to keep your information posted and updated even if you are not looking for a job.
It is good for companies because it provides a forum for the exchange of ideas and is linked to other social media channels. The LinkedIn blog has a feature that tweets new posts. You can list your contact information on LinkedIn and have other professionals find you and send messages.
My personal interest with the service is to stay in touch with all types of professional people, especially those involved in fluid power. For that reason, please see my profile and lets link in.