Folksonomies vs. controlled vocabularies

Sure the problem is not new, but interestingly enough I don't have the impression that the problem of tagging vs. controlled vocabularies has been truly addressed with an attempt to unify both views. An interesting contribution to this issue, which refers to the non-hierarchical nature of tags and asks about their scalability. What are your experiences concerning this? I am only starting to think about these issues, so any (random) thoughts or references to interesting publications about this are more than welcome!