Desirable Properties of Digital Libraries

Over time, libraries have had to adapt to the accumulation and curation of new media. We are all experiencing the introduction of e-books and other digital media but what are the properties we want to maintain or invent that will make such archives useful over time? What is the role of metadata? How should we be able to experience these media? What tools should be available to us for discovering relevant works? Could and should we be able to share our annotations? What does it mean to be a member of the equivalence class of all who have read/experienced a particular work? Can digital content be preserved over hundreds of years?