I just received my K-x yesterday. Have to say I'm impressed. I've shot with a Canon 20D and 5Dmk1, and Pentax K10D and this K-x just does such a great job on so many levels. I'm blown away by the high ISO performance even after expecting a lot. To my eyes it nearly matches the 5Dmk1, which is no small feat.
Anyhow, a couple of questions for you K-x owners:
1) Do you use the D-Range function? If so, have you found a "sweet spot" in terms of settings for the shadow compensation (i.e. low, medium or high)? Is there any disadvantage to using D-Range?
2) I've noticed a pretty consistent underexposure by 1/3 - 2/3 stop. This was true on my K10D as well, and I pretty much always had EC set to +1/3 or +2/3. I've only shot in very limited conditions so far, though, so it might not be true across the board.
Finally, here are a couple of quick shots (all taken with the FA50/1.4):