Go along this thread for what a K-x user has reported lately for the problem, with various comparison photos posted, and the related discussions thereafter:-
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=35716276
A conclusion can be quite conclusively made, that is, the blur issue seems to be existent for the K-x and at least many K-x units are affected. Shots that are taken with shutter speeds in between 1/60th to 1/400th (both not inclusive) suffer most from the blur, which can be easily seen when the pictures are viewed at full size.
And, also as pointed out by one of my Blog readers recently after the posting of my latest shootout test with the K-x, shots that were taken in the above suspected problematic Tv range do really have some blur, so that the pixel sharpness and image quality are degraded. Whilst I do agree that the pixel sharpness is not good for most of the test photos with the K-x in that particular test, I think I need to do a more systematic and scientific test with SR on and off and make comparison shots at nearly the same time so as to confirm the problem later on - that I will do it shortly, as soon as possible.
Btw, if the issue is really confirmed once again, it seems that it is just a design issue/latent defect more than a QC problem, as there have been so many K-x users whom have reported the same problem so far, already..
Read Also:-
Pentax SR Performance Tested and Compared (K-x Against Canon IS)
Summary Matrix for Equipment Tests and Reviews