While tagging is used heavily for taxonomy/folksonomy, it’s enjoyed some other interesting uses. This technique was new to me: identifying the key concepts in a speech by turning it into a tag cloud, in this case a cloud version of the President’s State of the Union Address.
This related site has a tag cloud of the countries mentioned in the Address.
Though it’s not literally a tag cloud, that application of tagging reminded me of the NewsMap, which I always find fascinating and yet for some reason hardly ever use.