Hm, maybe you have problems with front- or back-focusing? Try shooting a paper or something, from a ~45 degree above - so that it's clear where the lens actually focuses. (with kit lens, I'd say at 35mm at f/4, and camera using center point. Then when you zoom in on picture, there should be a sort of horizontal row of sharp letters)
Another issue I've had with K-x is that images appear kinda soft in-camera - probably because preview images in the camera are downsized. Most of them look much better on computer. Canon's entry-levels seem to behave another way around - their 3-inch screens look majestic, but some people I know that have T1i's, complained about pictures looking not as good on the computer. Oh well, can't say much since I don't have any personal experience with those.
I don't really have a kit lens, and the closest to it I've got is 16-45/4. It produces pretty sharp results. Like this:
K-x, ISO200, f/8, 1/125, 28m with DA 16-45/4, old Sunpak manual flash bounced from the ceiling, no sharpening applied
Crop:
Hope it helps!
Last edited by pbo; 12-21-2009 at 08:34 PM.