In my last position I needed to find certain professionals in other companies from time to time, and "cold call" them (no, nothing to do with marketing or recruitment). LinkedIn actually made that very easy, certainly easier than going in through the front door and the receptionist, and no one minded being contacted in that way. Sometimes I found a mutual connection to introduce me to the other person. Similarly, several people from ther businesses found and contacted me through LinkedIn. It's a good tool for business networking if you treat it as a service for just that, and limit your connections to people whom you actually know.
I have the same mixed feelings about LinkedIn as I have for Apple: I don't like their corporate policy but I do use their products because I find them very useful. As for them selling on the data: all of my data on their service is a matter of public record anyway. And that's how you should treat any social network: everything you put on there and (not unimportantly) what you do in there is public, mined and/or sold.