Binding user data files

Methods, systems, and apparatus, including computer program apparatus, implementing techniques for publishing, subscribing to, or playing live appliances. A live appliance includes a current virtual machine image. In publishing, a proxy file of a live appliance file type is provided to the publisher. The type is mapped to a live appliance player; so that when a proxy file is opened, the current virtual machine image is run. The player automatically binds a writeable file system external to the virtual machine image to the image to provide file storage that is accessible from within the virtual machine image and from a host operating system. The player also creates a subscription to the live appliance on the host computer if one does not exist when the proxy file is run. With the subscription, the player runs the then-current virtual machine image whenever the live appliance is run.