There are enough reviews and previews about this camera on usual review sites, here I'd just point out some obvious differences (or improvement) from the K-x:
1. AF seems to be quite a bit faster. I've no K-x w/ me to compare, but I did feel it's faster. Even a slow AF lens like DA35 macro is very responsive under low light condition.
2. AF point confirmation in viewfinder is a big plus over K-x.
3. AF assistant light is pretty effective under low light.
4. Bigger 3" LCD screen w/ 921k pixels resolution really makes big difference when viewing photos or doing live view
5. 6fps high speed continuous shooting is FAST!
6. AF adjustment (pity only one adjustment value for all lenses instead of one for each lens, but still it's better than w/o)
7. Auto alignment for handheld HDR (3x) photos might be useful to some users.
8. It looks a lot prettier (at least to me).
Had the camera for a few hours only, haven't got chance to use it under normal daylight yet, only have some random photos under room light or in coffee shop. The camera takes very clean and usable photos at ISO1600, it's pretty nice at ISO3200 too. With some post processing, even at ISO6400 isn't too bad.
Here I'd post a series of photos, all straight out of camera in RAW, converted by Pentax Digital Camera Utility 4 which comes with the camera, no other process done other than resize and sharpening as usual. The results would be much better if I'd do a bit post process. But since this is just for testing, I'd leave them as is.
Thanks to Denis for buying me dinner, I'd post some of his photos first (lens used: DA35 macro):
The high ISO can be expended to 25,600, but I didn't try that 'cause I'm sure I won't like the results at such high ISO anyway. Overall I'm very very pleased w/ the camera's high ISO performance.
It's nearly 10pm after I got home and took shower. Nothing much to shoot, so I decided to take a couple of photos of my new flat. Believe it or not, this is the very first time I actually took some photos of our new flat (all taken at ISO3200 w/ FA31):