Fantastic resource. If you do it right, and connect with the right people, eventually you won't have to apply for jobs because people will seek you out.
I just graduated and had about 5 or 6 interviews for jobs. I applied for them all, but within a week of all the interviews but one, I saw someone from that company had viewed my profile. Employers look... get a LinkedIn and update it.
I guess if you had been working in the same industry for 30 years you don't necessarily need one, but still... It couldn't hurt. Even if it doesn't directly help you, it could help someone else get a job because they are connected to you.