Quick primer for any readers who are not camera nerds: A particular filmstock's light sensitivity, or "speed," is referred to as "ISO." The more sensitive the stock, the higher the ISO number. The fastest motion picture filmstock available these days (last I checked, anyway) is ISO 500.
The Canon 7D's CMOS chip (which takes the place of film in this particular camera) has a user-adjustable ISO. It goes from 100 (fairly slow, requires a good bit of light) to 12,800 (ridiculously fast).
This increased light sensitivity comes at a price. In the film world, an image captured on a faster stock is grainier than one captured on a slower stock. In the digital world, faster chip settings lead to noisier images. So, to capture the cleanest image, more light is usually better. I say "usually" because there is such a thing as too much light. But that's a different discussion.
I mention all this because I shot a little bit of ISO 12,800 footage for Monster Hunt. It's noisy as hell, but still more detailed than what I was seeing with my naked eye. Here's a grab:
I'd say all that chroma noise makes this shot pretty much unusable. However, if you were shooting some low-light stuff with the intent on finishing in black and white...
...that might be kind of cool. It's cool enough that I'm interested in doing some more ISO 12,800 experiments at some point.
If you want to see video of the above examples, check it out on Vimeo.
And speaking of low-light shooting, I hope Noktor comes out with a Canon mount version of their f/0.95 50mm lens. That's some awesome glass for 750 bucks.