Stefano Mazzocchi: The problem is rather simple, really: words are not unique identifiers for concepts. Everybody knows this very well: synonyms exist in every language. So, all you need to start is to create unique identifiers for your tags, but if you don't do it well enough, it doesn't scale globally.
Randy: Great thoughts on folksology. I love his URN syntaxes. What's the difference between folksology and folksonomy? :)