Louis Rosenfeld on the limitations of folksonomies for businesses:

...As sites like Flickr and del.icio.us successfully utilize informal tags developed by communities of users, it's easy to say that the social networkers have figured out what the librarians haven't: a way to make metadata work in widely distributed and heretofore disconnected content collections.

Easy, but wrong: folksonomies are clearly compelling, supporting a serendipitous form of browsing that can be quite useful. But they don't support searching and other types of browsing nearly as well as tags from controlled vocabularies applied by professionals. Folksonomies aren't likely to organically arrive at preferred terms for concepts, or even evolve synonymous clusters. They're highly unlikely to develop beyond flat lists and accrue the broader and narrower term relationships that we see in thesauri.

...via elearningpost