We're working on an open-source distributed storage system that can also be used to easily share files. It also has p2p streaming download which is kind of fun to use. http://allmydata.org
I should add that we are not focusing on file-sharing. Our commercial model (.com) is based upon managed backup services. When we looked at the possibility of file-sharing as a service, we were quickly dissuaded by the amount of potential litigation we could face.