Curiosity is doing RAD - an instrument called Radiation Assessment Detector - while enroute to Mars. The purpose of RAD is to measure the amount of radiation that Cusiosity encounters in space and on Mars. Curiosity is the first rover to be so equipped and the data returned so far has been very valuable in seeing the radiation threat posed to astronauts in the new Orion crew vehicle.
RAD was originally planned to be turned on when on the surface but the Sun's activity made it worthwhile to gather the data while in interplanetary cruise mode. There have been five solar flare events that Curiosity has recorded data on.
Read More About It: http://science.nasa.gov/science-news/science-at-nasa/2012/02aug_rad2/
Sky Guy in VA Counting the Days to Mars Monday