If you're still wondering "what's all this fuss about tags", you have to read (or listen to) David Weinberger's succinct, charming and intelligent explanation. His conclusion:

Not only does this let us organize stuff in ways that make more sense to us, but we no longer have to act as if there's only one right way of understanding everything, or that authors and other authorities are the best judges of what things are about. And that's a big lesson.