The SAM chemistry lab aboard the rover is controlled by an Ubuntu operating system
Ubuntu is used in a lot of various fields and, judging from this short NASA clip, it's also used in controlling Curiosity on Mars.Curiosity has just celebrated its first anniversary on Mars and the NASA people made the appropriate arrangements so that it's organized properly.
NASA posted short video about the SAM instrument (Sample Analysis at Mars), which is the chemistry lab aboard the rover.
Before any experiments are being done on the surface of the red planet, the team of scientists from the Goddard Space Flight Center experimented with an identical SAM unit on Earth.
From the short video NASA provided, it seems that the computer used to send the data to the Curiosity rover is running a version of Ubuntu. The telltale signs are the buttons on the left side of the window manager, the Adwaita default theme, and the system icons in the top left corner.
Check out the video above for more details about SAM and Curiosity.