Out of all the panels, companies, presentations, and demo's that I saw in Scottsdale this week - the thing that had me thinking the most was a group discussion about 'Tagging' moderated by David Weinberger of Harvard's Berkman Center and Esther Dyson.

It was billed as a group discussion - and despite a moment when it could have become a series of presentations by a panel - it remained a discussion.

David Sifry of Technorati, Caterina Fake of Flickr, and Ross Mayfield added their insights into Tagging - but neither grabbed the mike and took over the show. Which was appropriate given the open-architecture nature of tagging itself.

For those of you just learning about tagging - it's a bottom up categorization system that basically lets users 'tag' a particular image or article with a word or phrase of their choosing.

Flickr has been playing with this a lot, and searching by words like "Apple" and "Uncle Jerry" result in interesting if not entirely predictable results.

What is perhaps the most interesting is how unformed tagging is as a taxonomy. There were lots of issues raised - about spam, about how the whole system to would scale and more and more people used different words for the same item, and how the lack of a governing body or central plan might make the whole system 'messy.' But that's kind of the beauty of it. It's open-source information architecture.. and as David suggested, it may actually fix itself as members perceive problems. For example, if people who are trying to point others to images of a Macintosh computer find that the tag "MAC" works better than the tag "Apple" - people may go in and adjust their tags to make the more successful.

Old media folks may find this whole system wildly free form. But take a minute and read the Wikipedia before you think that a self-governing content system won't work. wikipedia.

The basic premise of tagging is User-Generated Metadata.

The idea that messy data can begin to be shaped into useful new ways to focus, filter, and manage is great - and unformed. One point is - what are the alternatives. If you create a formal system (pull down menus, with a hyracy - "is the object a Place, Person or Thing, the - Car, Truck, or Bike, then red, blue or green" is a daunting task that would make most potential categorizers bail out. Remember the Dewy Decimal System from the library... imagine if you had to use a number system ever time you posted a picture. No way.

So tagging is the opposite of that. Messy. Easy. And it invites participation.

More on tagging in a bit.