I was asked? advised? not to let any dust gather on my camera's. Well, here's the proof that I don't!
My recent lightning shots were taken with the Coolpix 5700. I took 70 "frames" with it on the night of the 11th, and 98 "frames" with it on the night of the 18th. Definitely no dust gathering there.
Here are some shots taken with my N80. One of them has two satelite trails in it - that's a shot of Coma Borealis. Another is a shot of Lyra with my K1000 in the foreground - I was taking a hour long exposure of Polaris (the North Star) with the K1000. These were all taken on my back deck. All exposures are 30 seconds. The birght green in the trees is from a security light.