Let's try this again. The last time I tried to post this the whole site seemed to disappear...
The dust does show up more distinctly at smaller apertures. At wide apertures the light is coming from a larger area of the lens and spreads out more and fills in the shadows around the dust (the dust is on the glass plate in front of the sensor, so there is a little bit of depth). At smaller apertures the light is more collimated and gives a harder edge to the dust and makes it more visible.
As noted, it should be easy to test.
And I recently saw some interesting discussion about electrical charges in digital cameras at:
http://www.adobeforums.com/cgi-bin/w...@.3bc21cc7/127
John