I was very happy with my K20, and actually I essentially decided to forgo the K5, until I happened across a pricing error and was able to acquire one new in January for $750. Made a nanosecond decision and bought in for the price.
I like the K5 very much across all fronts. Its just that there are some aspects of the K20 I like so much better - enabling/disabling setting the Bracketing (the button on the back) , the placement of the formatting the SD card in the Menu, and a couple of other minor items.
On the positive side, I do like the movement of the external shutter release to the right hand side so that it does not interfere with a L bracket, the back menu camera setup state & status is wonderful along with the orientation change, the physical size is nice but the K20 was also very nice.
So, I guess forward progress. The sensor's ISO 80, dynamic range and shutter release location are alone worth the upgrade for me.
I have said this before, but I think I am set for a camera body.
If you are spending time drooling over a non-existent camera body - you are not out shooting enough!