A Twitter screensaver? :- Mac only

Yes, but it's not called twitter screensaver rather Twitterverse, here you can have the twitter world displayed which displays the messages in a thumbnail way, you know just like twitterworld
The procedures are for the Mac only first :- find the file (a quick Spotlight search for Twitterverse should do the trick), open your Desktop & Screen Saver preference pane, and then simply drag the Twitterverse.qtz file into the preview window of the Screen Saver preference pane. To get it downloading your friends' tweets, click the Options button, enter your username and password, and try it out.