It's one of those things where you'll get out what you put in to it. If you spend a lot of time from it, the stories of people generating business relationships and customers from it are very real. If you just make an account and never go back, you won't get any business from it.
So the question becomes whether or not you'll get business from it but is it the best use of your precious time. Minute for minute, I don't personally think it is, but perhaps I am either better at other things or bad at LinkedIn.