Made me wonder if it was actually amplifying the signal from the sensor or just boosting the number in software after digitisation (i.e. but before JPEGing - so nothing you couldn't do with a raw processor).
I've not checked the EXIF data on any of the sample images that are floating around (on flickr (http://www.flickr.com/groups/canondslr/discuss/72157606936093323/), for example) to see whether any of those are at ultra-high ISO; they all look pretty good, but then they're manufacturer sample images, so they would :). DPR and others will presumably have thorough reviews up in the near future, and we'll find out how good it is.
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