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).
That's all I can think of for now.