We have Edmodo at our school. It's like facebook for kids. They can only post on the wall (which I can monitor) so there is no secret messaging, or IMing. We use it for homework and whatnot.
This is what one of my students from last year posted a few days ago:
"HEY GUYS IF YOUR PARENTS R THERE GIVE THEM A BIG HUG AND A KISS AND TELL THEM THAT U LOVE THEM CAUSE I JUST TOLD MY REAL DAD THAT AND THAT CAUSE HE HAD TO LEAVE TO GO BACK OVER SEAS I AM PRETTY BUMBED OUT ABOUT IT HE JUST LEFT TODAY "
How sweet is she?