Quartz Composer is a wonderful tool to program some animations with Core Graphics. I made a simple example, showing a rotating sphere, on which I mapped an Earth background, and displaying an RSS feed on top.
You can download this example and install it as a screen saver.
Note: you don’t need to have Quartz Composer installed to play this screen saver:
1- download it from http://combal.free.fr/data/orbiting_earth_rss.qtz
2- save it in your library, in the ‘Screen Savers’ section
3- Launch the screen saver panel (System Preferences/Desktop & Screen Saver), you should be able to select the screen saver under the tab ‘others’. You can then configure it, and also change the RSS feeds (I set it to nature.com).