Just for kicks, I took my GH2 and PL45/2.8 into my son's room last night as he was getting ready to sleep and took a single, manually focused image at f/2.8, 1/10s (handheld), and ISO 12,800. The resulting image was more than 2 stops underexposed, so I pushed it to ~ ISO 65,000 equivalent* during RAW processing in Lightroom and converted to B&W.
The room was flat out dark, and I was surprised that I could even get enough information from the EVF to get a ballpark manual focus. As you can see, the focus point is on the pillow in front of my son.
Anyway, I was just amazed that I could get anything resembling an image at this ISO...
* I shot at ISO 12,800 and then pushed the exposure slider to +2 stops, which is ISO 51,200 equivalent. The resulting image was still dark, so I pushed it further using curves. This second push was probably less than half a stop, hence my estimate of ~ ISO 65,000 equivalent setting.