Library 2.0, tagging and the Tenenbaums

I've got a good sized DVD collection. My top 5 DVDs change all the time but there are a few with which I couldn't live without: The Royal Tenenbaums, Citizen Kane, Rushmore. My collection stretches to about 80 carefully selected items, all arranged alphabetically by title -a bit obsessive I know, but I used to work in a library. Alphabetically by title makes perfect sense to me, but depending on who you are, you might nit like my method of cataloging items- you might choose to group actors together, or use genre, or Director, or... or...
My point is that any system of organising things only works if it makes sense to you. Which is where tagging comes in. Using tags is a good way of letting users bring their own method or organisation to a collection of items: they can label things with their own keywords. These keywords can be gathered together across all users and displayed in the form of a cloud.
Our library management system Koha allows patrons to add their own tags to items from either the search results or details page. It's true library 2.0 but it has the benefit of allowing patrons to use a taxonomy or a folksonomy.