Skype and Learning

Spying on my teenage daughter, I had to smile as she was "skyping" her friends while doing homework.  Teenagers, do they not get enough of each other during the day?  To her credit, she was doing her work and, in fact, the kids often broke the chatter with questions about their homework.  Made me question how we could incorporate such a tool in the classroom.  Instead of penpals, we could have Skype-pals?  Has anyone used Skype in the classroom?