If you look to the left of this blog post you will see my tag cloud, which is basically a list, with the “importance” of tags (by number of times used) illustrated by the size of the font.
Wordle does something similar but looks very different.
Now unlike the tags on the left, the sizes here are not based on my blog, but some other indicator on the web; this is why windows is so large and molenet is so small compared to my own tag cloud.
However Wordle can use your del.icio.us tags, so the size of the tags is relevant to the number of bookmarks you have saved and the tags you have used.
It’s all just a bit of fun really, it really needs to be able to use other sites other than del.icio.us and the words need to be links.