I clearly missed a very interesting seminar. Thank heavens for saved material.
I think the biggest down side to tagging is that because it doesn't have controlled vocabulary, it doesn't always help you to find what you are looking for. I sometimes have to look back at my own stuff to see how I've tagged it, so that similar items have the same tag.
On the other hand, tags let you see how other people organize or at least catagorize information. It sometimes gives a new creative insight on known resources and information.