I've used LinkedIn for a number of years now. LinkedIn was one of the earliest attempts to adopt social media to business function. It is, in effect, an online contact management program. I have some 30+ contacts, mainly people I have worked with over the past years. My wife, on the other hand, works in recruiting and she uses the site to keep track of contacts; she has several hundred contacts. What kind of information is in the individual profile? Work info. Contact info. Relationships.
LinkedIn now has an app for iPhone users.