Reading through the Nielsen article ‘Organized Chaos: Global Data Harmonization’ which describes, in the context of categorization, the challenges faced by a single product being used for different purposes, it became very clear how awesome Internet tagging is. Tagging is effectively the ability to designate a single item to multiple categories.
The Nielsen article shows the image below as an example of the challenges of categorisation of a product used for multiple purposes.

Online Tags Advantages
On the Internet we are very fortunate that with tagging we may ‘assign’ as many relevant ‘categories’ to a single item as required. This eliminates the need for a single category being assigned. Of course there is still the ‘problem’ with tagging where two identical items may be described with different tags (and incorrect tags may be assigned). Tagging however is a significant step forward as opposed to single categorization.
Rich Snippets
Microformats / RDFa / Rich Snippets are beginning to be used by Search Engines to better identify similar or identical products. It is tackling this category constraint by allowing multiple categories. For example, a Canon EOS Rebel T1i is called a Canon EOS 500D in Europe. The hproduct identifier will therefore differ however brand, fn and category will enable Search Engines to better link the cameras as in fact being the same camera. The result is more accurate search results.
The Internet, with advances such as tagging, is certainly beginning to address the challenges faced through single categorization.
