I wrote this comment to the great post A cognitive analysis of tagging (or how the lower cognitive cost of tagging makes it popular) but it does not appear in the comments so I post it here.
Wow, I overenjoyed your short-enough essay. Extremely clear!
Might I suggest you 3 additional topics you might want to consider and include in your struggle for understanding? I would do it myself but I’ll never be able to write as clearly as you ;-)
1) Visit http://cloudalicio.us/tagcloud.php?url=http://boingboing.net/
The graph shows the evolution in time of the tags used to tag a specific URL (in this case http://boingboing.net). You may notice that in the beginning people were using more “blogs” and now people use more “blog”. This suggests people are moving from a category-like way of using del.icio.us (I put boingboing in the “blogs” folder that contains all the blogs) to a tag-like way of using del.icio.us (I name boingboing as a prototype of the class “blog”).
Someone was making this point (surely more clearly) on some blog but I could not find it again. Anyway this is true also for other blogs and this is real, thriving evidence.
2) At http://www.blumpy.org/tagwebs/ there is another “cognitive” approach to the tagweb (or tagspace or tagsphere).
I wrote about it at http://moloko.itc.it/paoloblog/archives/2005/02/04/tag_the_tag_tag_and_metadadaism.html
Jakob argues “a neuron in your brain is a lot like a tag in a tagweb”. A tagweb is a network of tags whose edges are the “this tag is tagged with this tag” relationship, for example he tags the tag “Victoria” with the tag “female”.
Will it be possible/useful to let users tag the tags themselves?
3) Of course it would be better to have people tagging stuff in a way that makes sense to them but, as soon as tags are public (everyone can see them), there is concern about tag spam (I tag something with a certain tag so that other people will be exposed to it). This is not a problem when tags are private, for example for the tag you use in your gmail account: no big deal in spamming yourself, no?
I wrote about it at
http://moloko.itc.it/paoloblog/archives/2005/01/29/what_is_tag_spam_or_better_tag_spam_exists.html (from where you can find interesting links). Or check the image at http://www.micropersuasion.com/2005/07/yahoo_myweb_bec.html
In order to make better tag systems (I think this is one of your goals), we must take into account this issue as well. Of course one simple solution would be to give you the possibility to see only resources tagged by friends (flickr and Y!MyWeb2.0 let you do this) or friends of friends, i.e. users deemed trustworthy by a simple and customizable trust metric. What do you think?