Personally, I've found value in it from the potential clients I've received (I'm a contractor) and the ability to look up just about anyone I may need to do business with. I use it professionally to get an overview of others like I use Wikipedia to get an overview of a topic.
I do know they have room to improve. I've been using the service since 2006 and have seen all manner of their silly practices. But as a well-known, professional network with a large userbase, I have yet to find a rivaling alternative.