Megan -- 1D III & EF 85mm f1.2 @ f1.2, ISO 3200, 1/2 stop under-exposed. Click for larger.
The reason I love fast lenses is because I hate flash. Flash destroys the atmosphere and gives lifeless pictures, especially when bounce flash is not available. I am not talking about multi-flash set up, but shooting at the moment when the picture opportunity arises. Also, the reason I like Canon because it has an arsenal of low light capable lenses, like the 24/35mm f1.4L, 50mm f1.0/1.2L, 85mm f1.2L, and the 200mm f1.8/2.0L. No other lens makers I know of makes so many f1.2/f1.4 and even f1.0 auto focus lenses. True, these lenses are crazy expensive, but at least you have an option.
Of all the Canon lenses I have, the 85mm f1.2L II is my favourite. It does not have the focus shift problem as the 50mm f1.2L at close range and is very sharp at f1.2. But, we expect it. Would you pay $2000 for a lens that you can't use at its maximum aperture? Many complain about the 85L's slow focus, especially for version one, but don't forget that it's a portrait lens. I wouldn't use it to shoot sports, and it's more than fast enough for me.
Ryan -- 1D III & EF 85mm f1.2L @ f1.2, ISO 3200. Click to enlarge.
The more I use the Canon 1D III, the more I like it. The focus works excellently, though not perfect, in extremely low light with low contrast objects. I am very relieved that I don't have any focus problems with this Blue-Dot version of the 1D III. It's ISO 3200 is cleaner than the Sony NEX-5N. The RAW files are just absolutely wonderful to work with. In fact, I am beginning to think that I don't need that 5D Mark II any more. That extra of a stop of better high ISO performance won't matter too much to me, as ISO 3200 is probably the highest I would use, and if I need wide angle, the 16-35mm is still wide enough for me at about 21mm equivalent at 16mm. For video, the NEX-5N (or the NEX-7 if it turns out as good as what Steve Huff says) would be more than good enough, as I don't even use it much.
Lone walk at night -- 1D III & EF 85mm f1.2L @ f1.2, ISO 1600.