Some guy has built a DIY GPS speed camera detector that warns him when he is going too fast in the vicinity of a speed camera. Pretty ingenious use of GPS, hit the link to see all the pictures and videos of the mod.
The detector has a display normally showing the current position and time. When the device detects that your vehicle is within ~500m from a camera it automatically switches to warning mode, blinking a warning text and the speed limit. The unit can hold up to 1600 camera positions in its memory and you can easily update the database with new data.