• Words are shown centered over the location where they were used. Larger words are more frequent.
• Related adjectives are shown in dark red underneath the word of interest.
• The time slider will start in play mode. Press the pause or play button to stop and start it or grab the handle and drag it.
• Select a different category of words to display with the selector control near the bottom left

• Casey Reas, Ben Fry, and the community around the wonderful tool Processing
• Twitter and all the users that create such interesting data
• The inspiration for the design came from the New York Times interactive feature on Twitter chatter during the Superbowl

There is a little more discussion about this in a weblog post on Neoformix.

This application depends on Java and may take a little while to start up.