From Magic Lantern
A video showing the difference between normal RAW and Dual ISO RAW can be seen below. Take a look at the shadow noise reduction in the Dual ISO RAW example, pretty remarkable. The person that made the video did so in a “worst case scenario” way, so your results should be dramatically better if you're actually trying to make great video.
In case you missed it, this is part of Magic Lantern increasing the dynamic range of the EOS 5D Mark III and EOS 7D by 3 stops using a dual ISO technique. You can read about it here.