If you are interested to have more sophisticated taxonomies in your SharePoint portal for tagging you can add another extension from the ISV market to enable knowledge networks. After categorizing items and documents with centrally managed, rule-based tree-style categories you can use additional content discovery compoents, e.g. category site navigation, category tree, A-Z index directory, tag clouds, related item links etc. to browse your knowledge network independend from the item's storage location. You an enable multiple different views to the portals data, e.g. based on organizational structure, products and services, geographically, timebased or by contributors.

Check it out:

www.sharepartxxl.com/.../taxonomy

Regards, Frank