If you've spent any time researching Canon's HD DSLR cameras, you've probably come across discussions of which of the cameras' ISO settings to use and which to avoid. There seems to be a common misconception out there, held by even some very well-regarded experts (http://www.zacuto.com/shootout, webisode 2, about 3 minutes in) that the cameras' "native ISO" or "true ISO" settings are the multiples of 160 (ISO 160, ISO, 320, ISO 640, etc), and that the rest of the ISO settings are produced digitally. This is not true. In fact the cameras' native ISO settings (that is, the settings that are derived from analog gain rather than digital exposure compensation) are the multiples of 100 (ISO 100, ISO 200, ISO 400, ISO 800, etc). However, that doesn't necessarily make them better.
I believe that much of the confusion comes from mis-analyzing tests such as these:
that clearly show that the 160-multiple ISO settings exhibit less noise than the 100-multiple ISO settings. Viewing these test results is often surprising to people because it goes against the conventional wisdom that the higher the ISO, the noisier the image will be, and the lower the ISO, the cleaner it will be. In fact, it is very surprising to learn that ISO 1250 can look on par with or even better than ISO 125. The natural assumption when looking at these tests is that the native ISOs must be the cleanest ones. This seems like a logical assumption at first, but it doesn't hold up when you look at it a little bit closer.