From the official website:
Wordle is a toy for generating “word clouds” from text that you provide. The clouds give greater prominence to words that appear more frequently in the source text. You can tweak your clouds with different fonts, layouts, and color schemes. The images you create with Wordle are yours to use however you like. You can print them out, or save them to the Wordle gallery to share with your friends.
[Editor's note: This awesome tool from Jonathan Feinberg, a researcher at IBM, displays tag clouds the "right" way by packing the words into the interstitial space between tags and rotating tags from the horizontal baseline. Johnathan uses simple bounding box logic to accomplish this. I will look into adding this to my Adobe Illustrator script (and perhaps bound the tags into a user-defined shape like a heart for Valentine's day).
If you look at the HTML tag cloud that is generated for my blog at the right sidebar you'll see a bunch of text on the same horizontal baselines. That type of tag cloud wastes a lot of space by not packing the words closer together. If there is a big word with small words on 1 line, there is a lot of wasted white space around the smaller words on that line. Fast but not pretty. And only horizontal. Up until now packed tag clouds have taken tedious hand-placement by an artist.
Now Wordle, a web Java applet will do that for you. The tag clouds can be saved as vector PDF by printing to that format in your web browser. This will generate a vector-outlined version of the tags (outlined fonts, not editable type) and in rich-black RGB color space so make sure to convert and clean-up in CMYK before publishing! There is no restriction on publishing the tag clouds for profit or otherwise. Seen on infosthetics.com.]