There does seem to be large swathes of users who are Doing LinkedIn Wrong. I constantly get invitations there from friends I already have on Facebook and Twitte

There does seem to be large swathes of users who are Doing LinkedIn Wrong. I constantly get invitations there from friends I already have on Facebook and Twitter, as well as IRL friends, college pals, etc. But no hard feelings—I only accept invitations from people who are in my business network or whose work relates to mine in some tangential way. LinkedIn is supposed to be the social network for business. Despite my disappointment with them on a number of levels and my low level of usage as a result, their proposition as a company isn't hard to grasp and I don't understand why it's so difficult for others to get it.