I've just upgraded my main camera to the same model's Mark II. The first shot doesn't seem that impressive, as it's a daylight shot of a familiar view. (There are noticeable differences in Lightroom, however.) But check this out:
That was shot at ISO-51200, 1/60th second at f/5.6. I mean, holy crap.
To put this into perspective: in order to take that shot with the Tri-X Pan film I used as a kid, I'd need a 2-second exposure at the same aperture—a 7-stop difference. The mind reels. Yes, it's grainy, but it's still crisp and accurate. (It's B&W because the sodium vapor street lamps don't produce any red light, so there's no way to correct the colors.)
The 7D I got four years ago was the first digital camera that was as good as the film cameras I used to use. This is the first one that's better.
Here are the stats, updated from 2011: