I thought you might be interested in some work I did to create a complete tagging system built on top of wordpress categories. No mods to core files or db needed. Check it out.

Tags can be helpful, but pulling tags out of text is redundant and adds no true value. In fact, Technorati’s keywords are still far more helpful for me than their Tags. Technorati keywords get pulled from the text and are representative of the content of the text being referenced. Tags applied by the creator of text content still falls in to the Cory Doctorow realm of “metacrap” as the author is trying to guess what others call something or what will draw other people to the content, which helps very few. It is a rare occasion where Technorati tags on general terms helps me find anything of use (often because it is incorrectly tagged), but Technorati tags work for very well for those social pre-determined event tags, like webvisions2005 or aon (for the always on network conference).

Where as consumer generated tags for their own retrieval are more helpful for themselves and others with the same vocabulary. These many times add value as they are terms not in the text. It is another point of view, which is where we get cross-discipline and cross-cultural value, among many other rich additions.