iTunes / Picasa type program for documents?

abolitiontheory writes: "On a crusade to regain control of my sprawling file structure recently, I consistently hit one dead end: document management. In the era of front end programs like Picasa and iTunes for images and music, is there no equivalent program for documents and/or PDFs? Key features I'm looking for are: thumbnail previews, visual interface, tagging and search capabilities, timeline view of some sort (date modified/created, etc.), and the ability to group documents into "albums" irrespective of their folder locations on the computer. Help me, Slashgods!"