Think of LinkedIn as your job, Facebook as a friend or family get-together, and Twitter as a bar or nightclub you frequent for happy hour.
I must admit, I have yet to find a real benefit to LinkedIn. I understand that "professionals" (e.g. business managers, doctors, teachers, professors) use it to interact and network with others in their respective fields while keeping their Family Feud game scores to friends and family. For me, the "purveyor of good times", there really isn't much boundary between work & play.
Which are you using more today?