As I’ve mentioned in the past, “information about information” is guaranteed to play an increasingly important role in how we manage our home lives and jobs. For evidence, we need only to look at the proliferation of metadata-based organizational constructs within Desktop and Web-based applications.
Search Folders, Smart Playlists, Virtual Folders, and Tags all group objects based on shared metadata and dynamically update their contents for efficient information retrieval through common attributes. In other words, files attributes in these instances “replace” typical hierarchical organization systems.
Though Windows Vista has shied away from a folder-less OS, the system does support the creation of “search folders”.
“For example, you could design a search for all documents that are authored by "John" and that contain the word "project." This search, titled "Author John/Keyword Project" is saved as a Search Folder. When you open this Search Folder, the search runs, and you see the results immediately. As you add more files to your computer that have the author John and contain the word "project," those files will also appear in the Search Folder alongside the other matching files, regardless of where they are physically saved on your PC.” –Windows Vista
Smart Lists in many of Apple’s applications work in a similar manner:
“Simply indicate your desired criteria — like all the rock songs you’ve added to your library in the past month, songs you’ve listened to more than 10 times and so on — and iTunes does the rest. iTunes automatically finds the songs that match your rules and creates a playlist.” –Apple iTunes
Groups of tags within sites like del.icio.us are also utilized for meta-data based organization.
“Tagging can be a whole lot easier and more flexible than fitting your information into preconceived categories. If you want to post an article about a little known Greek philosopher, just tag it with "philosophy greece" or whatever other tags you'd want to use to find it again. You don't have to rely on the designer of the system to provide you with category for Greek philosophy.” –Del.icio.us