Invitations

In just the last week, I've been invited to sign up to or join:

1. Linkedln
2. Pownce
3. Facebook

Hey, thanks for the thoughts everyone (and a special hat tip to Mike, who over the years has invited me to sign up to dozens of services of one sort or another. Probably none of which I have taken up)

Now a question - what are all these things? (I mean, I could look I suppose, but I have a history of looking & not seeing the point anyway, so 25 words or less on what these are & why I need them might help. I mean, I'm just not an early adopter of new gizmos, like some people I know.)

But if it means more txts, notifications, or emails...