There is a nice straightforward article by Thomas Vander Wal on Zdnet blogs about Taxonomies.  In it he explains why - as many of us know - that withi an organisation it should not be a choice between traditional taxonomies OR social tagging/folksonomies, but that it should be an AND choice with the latter informing and feeding into the former.

The fact that a Taxonomy should be a living thing is one I have seen overlooked in companies before.

 Vander Wal uses the following table to show how by combining them each of their strengths accounts for the other’s deficiencies.

Good article. Well worth a read.