Folksonomies and implementations
Peter worries about and wishes for a folksonomizer service, something that would allow the users to tag everything.
And suddenly, I find freetag, and open source tagging module for PHP/MySQL databases.
I don’t know how close this thing goes to all the requirements and definitions that Peter enumerates, but it is certainly worth a look by those enlightened experts out there.
How big and complex is our metadata turning out to be? We get out of the context and explain one and each of the postings that we write. There is some business opportunity there, but I do not know what, exactly.
UPDATE: Upon a more detailed inspection, I found that Gadgetopia's Deane is talking about tags as well, and then points to implementation of tags in SQL as well as a screencast by Jon Udell on delicious.
And here is a nice google scholar search on the subject; that is right, empty.