Let's see what our great measurbator Falk of the Lumo's Lab says:-
Full Report: http://www.falklumo.com/lumolabs/articles/k5shutter/
Short Summary: http://falklumo.blogspot.com/2010/12/lumolabs-pentax-k-5-shutter.html
So, all the formulae, graphs and plot charts are just too difficult to me, whom as an unqualified measurbator when compared to Falk! ;-D But then we can simply see and read his conclusion and comments, which I think could be easily understood!
"The shutter-induced blur in the Pentax K-5 is measurable but it should be small enough to be of no concern in day to day photography. The absolute magnitude of the effect sits halfway in between a K20D which has almost no measurable effect and a K-7 which exhibits an effect large enough to make some people notice in their work.
The matter may now have reached a satisfactory state with the K-5. But there remains work to be done for Pentax to fully understand and eliminate any unnecessary effects which compromise image sharpness.
It would be interesting to test another camera with fast shutter (like a D300s) to compare the absolute magnitude of the shutter blur effect which is never zero. Esp. at ~1/160 s. Ideally, vendors would measure it and make part of their cameras' shutter specification."