by Thomas Vander Wal himself, getting alienated by what wikipedia made out of his initial concept:
"Deriving Value from Folksonomy: There tremendous value that can be derived from this personal tagging when viewing it as a collective when you have the three needed data points in a folksonomy tool: 1) the person tagging; 2) the object being tagged as its own entity; and 3) the tag being used on that object. Flattening the three layers in a tool in any way makes that tool far less valuable for finding information. But keeping the three data elements you can use two of the elements to find a third element, which has value. If you know the object (in del.icio.us it is the web page being tagged) and the tag you can find other individuals who use the same tag on that object, which may lead (if a little more investigation) to somebody who has the same interest and vocabulary as you do. That person can become a filter for items on which they use that tag. You then know an individual and a tag combination to follow. The key is knowing who and what specifically is being tagged."
semantic triangulation. beautiful