I think I remember Martin Brundle saying they had some sort of wiper that comes across the camera to clean it from bugs or water etc.
I think I'm right in saying the onboard cameras aren't HD yet due to some dispute with the teams about weight/size? I think the onboard shots could look stunning in HD, at the minute I notice HD the most when looking at the presenters before/after the race....
Anyway, whatever the cameras actually are I'm sure they're bloody expensive.