I like nothing more than shooting in available light. It was always a fight with my K10d, balancing ISO and aperture and pushing shutter speed to move the exposure to the right of the histogram, often resulting in motion blur.
K-5 Seems to solve all that! These were shot at iso 6400, probably -1/3 ev on the exposure as well as I had to lighten them up a little in post. This is absolutely the body I have been waiting for from Pentax. It plays really nicely with the 31mm as well, these were all shot around f2 I think. Shake reduction seems improved over the K10d as well, making this a REAL killer in low light situations, imho.
At the end of the day I just love the results coming from the camera, that's all there is to it.
The above are linked from Smugmug where I store my originals...below is a sharpened version of Racket the dog