In Metadata, Semiotics, and the Tower of Babel, Tim Oren rants against some of the assumptions behind the metadata bubblet which Joi Ito hinted at in his If I were Microsoft post. It is kind of ironic that Tim used the Semiotic wand to blast the Shangri-la illusion off the Tower of Metadata Babel because people had many different interpretations of Joi's post.
Symbols are just containers for semantics. If you put cookies in one, people know them as jar with cookies and identify it by its shape and location. As soon as you have one jar, you will have many so people invented ways to refer to each jar by name (cookie jar) and distinguish it by sight (it has a picture of cookies carved on it).
Semiotics is all about problems of jar selection. While size and shape of a jar limit what can be stored inside it, there are enough leeways for people to use the jars for wide variety of purposes.
In Korea, there is a specially shaped jar for urine so one doesn't have to go outside in the middle of the night to take a leak. It's a beautifully shaped jar. Now imagine what would happen if an American came upon the jar. Chances are pretty good that he would see a cookie jar, a jarring example of semiotics.
So Joi was musing about Microsoft monopolizing the emerging jar market to gain an upper hand on Google which cornered the market on baskets. Tim disagrees because people can put anything in jars regardless of the picture or label on the jar which will cause confusion like the Ecstasy test result mixup.
I am somewhere in between. I believe two common forms of human nature, conformity and mimicry, allow sufficiently large and reasonably coherent set of metadata to be created, if not by design, then by popularity (see Emergent Markup Languages).