I've never understood the appeal of tagging. How is going through all my files and adding the appropriate tags to each one any easier/faster/more convenient than just putting them in a folder in the first place? Sure you can have multiple tags per file, but every one of the very few times I've had to find files based on some kind of arbitrary metadata, it's something that I never thought to use as a tag (eg. i have photos tagged with location and date, but i need to find pictures of my brother).
i do see the value in social tagging where it's likely someone else has already done the dirty work, but for my own stuff? Never.