Märgendamine ja folksonoomia

This week's excirsise: "Otsige veebist kaks näidet folksonoomia kohta - üks selline, kus see väga hästi töötab, ning teine, kus see eriti ei taha toimida."

The term "folksonomy" is new to me. I will try to give the definition in my own words. It is a way of categorizing information using special words, called tags. But when does tagging information work?
A bad example where tags can not work are blog hosting websites, like Digg or Blogger. If you are searching for some blogs through a search engine, then it already will find you some material based on the content of an article. Instead of using tag words, the words can be used in the article itself.
A good example, where tagging works is a website for storing pictures. By this, I mean something like Flickr or Picasa. Picture filenames can be "DSC00001.JPG", or similar, but for a search engine it is not clear what the picture contains. Ofcourse, algorithms can detect faces and the color of the picture. But what better way to describe a picture by tagging it something like "City of London skyline from London City Hall - Oct 2008.jpg". This will make the picture easier to discover.