I'm loving my K-7. It's a HUGE step up from the original Canon DRebel (300D). The lower noise sensor of the K-X would certainly be nice, but a lot (not all) of that disparity is mitigated by shooting RAW.
My guess is the next iteration (probably another 1.5 years away) will have a much improved, non-samsung sensor.
Meh, it's not like the K7's IQ is bad either. It's not that good at high iso...but at low iso it's good...imho at base iso it looks better than the K-X and captures a little more detail, so meh. Just depends on what you use more I guess. I think the K7 is great for someone who does a lot of hiking or outdoors stuff. The body is really well built and solid and it has just about every feature imaginable hehe...
I haven't actually played with a K-X, but it looks like a damn nice low price body. (Just fyi I shoot Canon--a 7d and a 450d). However the lack of af points in the viewfinder would be a deal breaker for me though I think.
The K-X's high iso has a dirty little secret though. It only looks clean because the camera is throwing away a TON of color information. I don't know if this is software NR or on-chip hardware RAW NR (that sony has been known to use in the past).
For example, I've seen the claim that the K-X's iso 6400 is better than the D300s iso 6400...and on the surface it does look a bit cleaner...however...look at this:
Nikon:
http://75.126.132.154/PRODS/D300S/FULLRES/D300ShSLI6400_NR_NORM.JPG
K-X:
http://75.126.132.154/PRODS/KX/FULLRES/KXhSLI06400_NR2D.JPG
The proportional scale on this image illustrates what the K-X does. The blue letters on the scale (which are still blue in the Nikon image, like they should be) are now black. The chroma info is completely destroyed.
Or compare it's iso 12.8k output vs the 7d's for example...same thing with the blue letters there. Look at the red letters on the bottle that say "Samuel Smith's is a small, independent British brewery". The red letters have been completely desaturated in the K-X image.
So it's not that the sensor is awesome at high iso unfortunately. In reality there is some very very destructive noise reduction going on behind the scenes in the chroma channel. In most cases it looks like the output is pretty good though, but still--people should know what is really going on. I don't know whether this NR is applied to the RAW files or not though (like some Sony cameras do/did).