I posted a simple pair of photos from my own experiments not too long ago,
here. Since I sold my K100D, my comparison is between the *ist DS and the K10D.
I have long contended that the claim the K10D does a lousy job at anything over ISO-E 400 is a big exaggeration. In my informal tests, the K10D doesn't do much worse than the K100D I used to have or the *ist DS I have now. I shoot a lot of low-light photos. When I switched from the K100D to the K10D I simply didn't notice any sudden, dramatic degradation in the quality of my photos due to noise.
I do wish the K10D could produce noise-free images in low-light at ISO-E 1600. I gather that some other cameras do a better job. I just don't find it to be a huge problem.
Will