The calendar would allow me to track modifications and deadlines for documents that are being produced as well as provide reminder of reviews that are required from people that I have shared documents with.

Documents and files that are shared could also have deadlines added to them allowing something to be shared with peers or to the public for a limited time only.  Special offers, etc.  Once a document is expired a link to the "latest version" or "alternate" could be provided.

The calendar feature would provide a widget that could be placed on a personal blog and a facebook application allowing people to view items that you allow access to.  The widget and shared calendar would allow the creation and sharing of events that could be registered for.