I might be remembering wrong, but I think in the very early days of facebook there was something that allowed you to file share through it that Mark had added in. I believe it was taken out though because the hostility that would have come from the entertainment industry wasn't worth the risk.
It was called Wirehog and was a seperate website which was linked to Facebook users accounts. Sean Parker encouraged Mark to shut it down (although Mark seemed interested in the idea at the time) because he saw another Napster situation coming and knew Facebook could be big without the hassle.
Looking for the link.