More people are tagging content organizing it the way they see fit. Using sites like deli.cio.us, flickr, youtube, and technorati, people are indexing things and sharing what they’ve categorized. It may be time to start using these things yourself to better understand it for your own site. (Of course you can also bookmark and tag your own site.)
It is also possible to encourage people to tag your site. Ask your webmaster if it’s appropriate to add to your site.