I too am considering doing this swap.
Pretty much all my gear is lightweight/tiny but the K10D is sooooo heavy.
Here we are again, Marc, talking deal breakers
For me...the lack of a grip might be *the* deal breaker since I have big hands. It makes the K10D comfortable but also bigger and heavier. I refuse to use the camera without it...the pinky finger sticking off the camera is incredibly fatiguing to my hand (kind weird how bad it really is).
I've never held a K-m so I don't know if it'll feel right. My Rebel 300D was a little bigger than the 350/400/450D's. The 300 felt nice...the others, too small. So I think the feel is my #1 deal breaker.
Also kinda worried about the viewfinder. It needs to manually focus well.
But the K-x will be worth it if the high ISO is usuable. I keep away from even 800 on my K10D.
I don't see any negs of the K-x besides it might be too small for me and the viewfinder might not be bright enough. Weather sealing is nice...but I don't have any DA* lenses as of yet