I have been very pleased with the shots from my new K20D which replaces a Canon EOS 350D... it's in a different league. The controls are intuitive and the ergonomics are good (nice solid rubbery grip). Factors that affected my choice: 14Mpx, flash synch socket, anti-shake, new-technology CMOS sensor, sensor cleaning, water/dust resistant, capability of accepting a wide range of Pentax fit lenses. If getting a short zoom lens be sure to specify the Pentax 18-55 VERSION 2 which is superior to its predecessor. I bought this plus the Pentax SMC 55-300mm and a tele-converter, they are all performing well. I did some anti-shake tests and despite being criticised in reviews as crude compared to Alpha and Nikon competitors, I judged its peformance to be absolutely excellent.
I'd say that while the build quality and optics are superior to the Canon, the metering and the autofocus are inferior, I have 1/3 stop overexposure dialled in routinely and have ground my teeth in frustration on occasion when the long zoom has chosen to autofocus in the wrong direction winding all the way to infinity before winding all the way back to achieve a focus. These days I manually focus part way to the subject to give the system a leg-up. I tend not to need or use Live View ... if I regarded this as essential I'd have probably chosen the Alpha 300 with its fancy (fragile?) swivelling screen. The Live View on the K20D is not great, I've used it once for setting up the camera on a tripod.
I conducted a series of tests on the tripod to see if there was an optimum ISO setting and found that 800 and 1600 gave the best results, indeed 1600 is superior with virtually zero noise intruding and good contrast, 3200 is for emergency use only ... noisy enough to spoil the image. I tend to use 800 most of the time but go to 1600 with confidence if the need arises.
The image below shows the full frame with sample area shown plus inserted clips at full resolution for each ISO speed. Hope this helps, get to me via 'personal message' if you want anything else.