"Tagging" your favorite books

Here's something I just learned about: tagging. If you have a favorite author or book genre, you can go on different websites like Amazon.com (www.Amazon.com) or the Ann Arbor District Library (http://www.aadl.org/sopac/tagcloud) and just click on a tag, which is basically a key word. You are then linked to other great books or movies with similar themes! One more step are tag clouds, where the size of the tags is determined by their popularity. The more popular a key word is, the bigger the word is. Very interesting and useful, though I personally would rather just peruse the bookshelves of my favorite library or bookstore. :)