What is the Tag cloud?
Tag clouds are well known on blogs or simlar websites. This concept for organizing a medialibrary is afaik not often used.
In the Nemp tag cloud all meta data like "Artist", "Album", "Year", "Genre" are all treated as "Tags". Some more are automatically created (like "decade"). The most common used are displayed in the cloud. How many tags are displayed, depends on the size of the window.
You can navigate through the cloud by doubleclick on one tag. Nemp will the create a new tag cloud, considering only tracks that contain the selected tag.
You can add arbitrary tags to the tracks in your library (like "summer holiday 2005" or "mums last birthday") . Furthermore, you can use the LastFM webservice to get additional tags that have been added by the LastFM community.