Plone is currently serving up the content and forums for "NASA's Mars Rover website":http://mars.telascience.org/home - and is a good example of a site that manages its content with Plone.
On the site, you can also download the software that NASA runs to control the rover itself, and play around with it. The rover does not run Plone, unfortunately. ;)
The project was put together by some members of the Plone community together with people from NASA, and the site was so popular that Sun had to provide the server on a network with more bandwidth. More details are also found in "an article on CNET":http://news.com.com/2100-1007_3-5142220.html which discusses some of the software details on the rover.
I think this is beyond cool, and would like to congratulate "Alan and the others":http://mars.telascience.org/acknowledgements involved with this site.
"Check out the site":http://mars.telascience.org/home