You can use either use some text you type or copy out and paste in, any valid blog address or its feed, and even your del.icio.us user name (in this case it fetches your tags.)
These are some quick examples, using the first sonnet by William Shakespeare (top image), and tags from some of my online projects. You can click any of these pictures to see a bigger sample while it is generated on the fly. Guess where does this one come from?
Try it out by yourself with any browser (Java plugin necessary), chez Wordle.