It's a load of old bollocks is LinkedIn. I'm only on it as when I left work someone asked me to "to keep in touch" (like email and telephone's don't work anymore FFS). Now nigh on every sodding day I get reminded about people's work anniversaries, that they've endorsed me for some supposed skill or even their birthdays. And now it is sending me details of jobs I might want - I don't.
FWIW two ever so important rules with LinkedIn:
1. Never let it invite all your email address book - you will annoy most of your friends.
2. Never ever ever ever let it link to your e-calendar. It will add loads of peoples birthdays into your calendar as read only entries you cannot delete or edit.