There are rumours that every digital SLR out there suffers from a shutter-induced blur. This phenomenon manifests itself in blurred images when using short exposure times, which should normally deliver images free of motion blur (like 1/100s with a focal length of 20 mm).
Some cameras, such as the Pentax K-7, have been reported to suffer particularly from this problem, which has become to be known as the "shutter bug". The shutter bug only appears at specific exposure times, reportedly at 1/80 to 1/125 s. Exposure times slower or faster than these do not exhibit any unusual blur.
I own a K-7, and I can hardly observe a problem in day-to-day usage. But to be sure, I wrote a small program which can measure the blur in digital images: Shutterdebugger.
Shutterdebugger is a small program written in python, to be operated from the command line. It depends on:
Shutterdebugger is not optimized for user friendlyness. It has been tested only by me, and only on my machine. I have no idea whether it will work for others, on other machines, with other cameras than mine, or on operating systems other than OpenSuse. But your feedback is highly appreciated.
In its current state, shutterdebugger produces a plot which is not very beautiful, and some might even say that it is not very informative. However, for that plot was enough to be convinced that my camera is not affected by the shutter bug, and this was where I stopped. If you are not satisfied with the current state, feel invited to improve on it. This is open source after all!
If you lack programming skills, you can send me your suggestions for improvement, and I will try to implement them. But please understand that this is a side project of mine that I manage in my free time, which I usually prefer to spend taking photos. In the end, I would advice you to do the same ;)