Flickr picture (being the nosy people we are, we clicked the link). What we found surprised us -- a Twitter Quartz Composer composition was included as a part of the Mac OS X developer tools for Leopard. "Twitterverse," when tweaked right, can be used as an OS X screen saver and display all of your friends tweets in a graphical way.
You can find this Quartz composition in the ~/Developer/Examples/Quartz Composer/Compositions/XML/The Twitterverse/The Twitterverse.qtz. If you want to add it as a screen saver, just drag it onto the preview in the "Screen Saver" part of the Desktop & Screen Saver preference pane (in System Preferences.app). You can then add your username / password in the screen saver options.