You can copy-paste text into a text box and ask Wordle to analyze it and produce a word cloud, where the size of each word reflects how often it appears in the analyzed text. Alternatively, you can point Wordle to a del.icio.us account and it will produce the corresponding tag cloud. Here's my the tag cloud for my top 100 del.icio.us tags:
Pretty obvious what my favorite tag is... Incidentally, I haven't been using del.icio.us a lot lately. I've been using Diigo instead, which in addition to social bookmarking allows you to highlight and save text clippings from a web page.
By default Wordle analyzes the 150 most frequent words, but you can tweak this number to produce sparser or denser word clouds. You can also choose to ignore capitalization and show only lowercase words, which eliminates spurious duplicates.
Wordle conveniently removes frequently used words such as "the" or "is" unless you explicitly request it to show them.
Wordle randomly chooses a font and a color scheme, but these can also be changed by the user. Many of the available fonts are gorgeous, whereas the color scheme offering could be more varied.
After del.icio.us, I decide to generate a word cloud for my Twitter tweets, but I first had to obtain my full set of tweets. Unfortunately I couldn't find a way to download my own tweets from Twitter, which is unfortunate. Twitter, if you're listening, please set my data free (or correct me if I'm wrong). Google Reader and Gmail do it; Typepad does it; Bloglines does it; so should you.
Luckily I found TweetDumpr, a simple webapp that exports your tweets into a CSV text file. With some simple parsing and cleanup, I got a clean text file with all my tweets, which I copy-pasted into Wordle. Here's my Twitter top 100 word cloud:
Unfortunately Wordle currently seems to be down for maintenance, with the following notice: "I am tinkering with Wordle... Don't fret! We'll be back."